In the aftermath of the Spellplague and in particular after the reconstitution and withdrawal of the Harpers into secrecy the bards of Faerûn lost much of their mystique, becoming targets for those who would prefer that certain things were not sung of or that certain stories were never told.
After a rash of deaths in the North and in the Heartlands, a group of worshippers of Oghma connected to New Olamn decided that enough was enough. Led by a convert from the fabled land of Zakhara who had started life in the Brotherhood of the Flame but had found her true calling in the Oghman Church they founded a sect dedicated to hunting down those who would blaspheme against The Binder by silencing the voices of His agents.
The Order of the Bloodied Quill is an order of avengers, many either multi-classed as bards, wizards or sorcerers or multi-classed as avengers. Anyone who threatens, kills or imprisons bards, priests of the Binder or sages for spreading or discovering knowledge may very well come to the attention of the Order: several lords have been found very dead with a feather dipped in their blood by their side. Book burning isn't encouraged either: three weeks after a Sembian governor burned a sage's library for publicly questioning his claims about his family history he perished in a pillar of flame while holding court.
Over the years the Bloodquills have developed a special place in their heart for the followers of Cyric: a foul, dark, twisted place. The consider the Prince of Lies and his minions as a cancerous growth on knowledge that needs to be cut out. Even the most good-aligned, mildest member of the Order will show no mercy to Cyric's priesthood.
Officially, both of the churches of Oghma consider the Order to be aposates, acting without the blessing or support of either the church or the god. In practice, too many prelates owe their lives to Bloodquills and many temples quietly support them.
The Order of the Bloodied Quill has clashed with the authorities in several places - notably Cormyr - and aren't very popular.
Members operate independently, doing their duties as they fit, though they may receive suggestions from either superiors or may act on the concerns of the clergy - it would not be unusual for the clergy to post condemnations of acts against the voices of Oghma in the hope that the Order would take action.
The Order has no real base - members are recruited and trained by senior members in secret and often as an adjunct to other training or study - but tends to cluster around the great libraries of Faerûn and there are secret Chapters in Waterdeep, Highmoon, and Candlekeep. Membership is probably around a hundred active members. Rites of Investiture are carried out in remote places sacred to the Binder, where a dozen Bloodquills, led by a senior member, carry out the ritual.
As followers of Oghma are often called Namers so a paragon path that allows them to utilize truenames might be appropriate.
The origin story feels very organic and gives proper weight to their name. Same with the quill dipped in blood and tossed at the offender's corpse...this comes off as bad*ss when it could have come off as cliche. 
I really want to play one of these. Good job!I did quirk an eyebrow at the "remote places sacred to the Binder" part. Broadly speaking, secret places no one knows of or can go to kind of grates against Oghman flavor imho, as well as published Oghman lore that I can recall.
("Hey, let's go to that new library dedicated to Oghma." "Sorry, no one really knows where it's at. I think they built it over in the swamps somewhere.")
Hidden caches of books for wandering priests might be handy, a hermit's cottage where a lone individual toils at tinkering and scribing makes sense, and Candlekeep itself is fairly remote and has off-limits areas within it, but unless I'm misreading none of these seem to be the type of place you are implying. Perhaps with the nature of the order they simply create temporary ritual spaces in remote areas. What did you have in mind here?
Midnight in the Reading Room would be more appropriate, wouldn't it?
Yes, copies could assuage the essential doctrinal issue I believe. Other than that, let the order be as different from the established churches as you can imagine. I'm not sure I dig one central "Dark Library" though. What really hooked me about your write-up was the vigilante feel and I'd be afraid too tight of a network/structure would take away from that. Of course, you may be going for a different feel than I happen to have latched onto, which of course is completely cool. (I hesitate to give examples b/c I don't want to throw off your creative momentum!)
Questions: Is the schism in the church relevant at all to a Bloodquill's mindset? And how do commoners and the younger clergy (of either branch) react to the order? I ask the latter because you say the Bloodquills are unpopular, but also mention churches posting notices in hopes that the order will bring them vengeance.
Hello! I love this! :DI'm not sure about the Dark Library either, except as a hiding place and ceremonial centre but I've now got a vision of a huge circular reading room in dark wood lined with levels and levels of shelving. A windowless, taller, circular version of the Long Room. I'm thinking of it as equivalent to a secret keep where most members visit once to take their vows and whatever ruling council there is meets, holds court and hands down occasional judgements. I have a vision of hooded Librarians adminstering terrible oaths by the light of flickering hooded lanterns (no open flames allowed!).