Is it even possible? I am building a warlock that already does some pretty good damage, but If I could find a way to use another eldritch blast, it would beef it up considerably.
It needs to be available pre-epic, and I have already added the quicken spell like ability in the build, I am looking for away to get a third blast.
You could get someone to turn you into a choker. Also note that demonbinder is another way to get a swift action eldritch blast. That requires you to be a drow, but if you can use the 0 LA version of drow or buy off the LA it might be good.
Excellent. Where can I find the Demonbinder class?
Take white raven tactics from ToB, make sure you have a cohort that also has it...
- your turn: use the blast & white raven tactics as swift action
- your cohorts turn: he does no matter what and uses white raven tactics as swift action
- your turn again: you use the blast, and again, quickend
How much of dip do I need to make to get that ability? I am trying to stay pretty close to full progression.
Either 3 feats (leadership, martial study 2 times), or 2 feats (leadership & martial study) and an itemslot (for crown of white ravens, 1500gc), or 1 feat (leadership) and a classlevel in crusader or warblade.
You can pull this off with a willing partymember as well, without the need for leadership.
Excellent. Where can I find the Demonbinder class?
It's from Drow of the Underdark and there is an excerpt. Take note of the damnation points ability and the marilith option of the demonbind ability.
Right, I can probably do that, especially since leadership is the most broken feat in the game.
Now that my warlock can kill anything ever printed in a fraction of a round, I have come across a serious flaw in my build, what if I lose Initiative? I am going to have a high dex and probably imp. Init. too, but just in case, how can I help beef up my defenses? Since after I post my build people are likely to mention the survivability of the build isn't much better than the average lock.
So my next question is, how should, and how can, I make my Warlock last long enough to live if he doesn't go first?
Never mind, didn't read the OP right.
I don't know if Pathfinder variants are an option for you ?
But the Pathfinder version of Warlock can take "arcane flurry" at 12th level.
The bolts do half damage, but you can fire of a number of bolts per round equal to 1/4 your caster level 
In addition, Arcane bolt is an (Su) so no spell resistance nightmares, and has a greatly improved range 
It's in Tome of Secrets.....check it out.
You could use the eldritch glaive invocation from dragon magic. It turns your eldritch blast into a glaive and lets you make more attacks with it if your base attack bonus allows it. Not sure if this is what you're looking for though, but it can do some very nice damage. If you're interested search for some glaivelock builds.
What level is your Warlock?
If you were lvl 3 then I think I may beable to help.
Probly not the best to do but it sounds fun atleast 
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Warlock 3, Cleric 4, ED 10, XXX (You can 3 more Warlock or 3 more Cleric), Personally I would go 3 more Cleric to get 9th lvl spells.
If I was going for a Blaster from Frak type. I would do a Warlock 3, Wizard 3, ET 10. Then add 4 on either Warlock or Wizard side. Now your a decent DPSer.
I personally would go Cleric side because with that you can buff yourself up and in turn increase your effectiveness as a Warlock I believe. If you cant, then I would go Wizard.
Race, depending on what you do and if your allowed an LA buy off, You could go a Cleric spring attack healer with a Quickling. Cant go wrong with that
Right now though my race choices for these 2 types would be a Quickling for its high dex or a Pixie for its more spread out abilities. If you go cleric, grab monks belt to get Wis to AC.
If you wanted too you could even go with a Dwarf Warlock, Wizard/cleric, then one of the corresponding PrC (ED/ET), then if your going past lvl 20, add in Fist of the Forest somewhere, maybe Monk to boot and your good to go . Toss in Deep Warden 2. Pump your Con up, Your Wis up. Maybe toss in Saint. Now you got your Con to AC 2x, Wis to AC 2x. You got your int/wis hopefully high around 25-30 or something. Now look at ya , high AC, Which stacks in shapechange mode . Ohh I just got the shivers . Taking a year or 2 off from offering DND advice has gotten me the shivers .
If you wanted too you could try a trick to get Abj Champ 5, Arcane Disciple to get Divine power going for you. Now toss Divine power on ya.
Your looking at Max BAB (Thanks to Divine Power), and Max CL (Thanks to the 5th lvl Abj Champ ability)
Let me explain. Given power gives you BAB based on your level. Abj Champ gives you a CL based off of your BAB which should be maxxed . Hope this helps further .
Hope this helps