And yes all their minis are pewter.
As for finding someone to paint it, best bet would be to a gamer store near you, sometimes you will find people with adds willing to paint figures.
Reaper Miniatures makes their products out of white metal, i.e., "pewter" (mostly tin with a bit of antimony and other stuff). Uglunuk is rather large for a regular-sized character, even a goliath (not so much for a goliath, but still a bit).
As shown Here, on the Reaper figure finder, the mini comes in three parts - the body, the axe with the hands attached, and the plastic base. You'll need to glue them together with cyanoacrylate (superglue) and then paint it (usually with acrylic paints).
Changing the weapon might be a bit difficult, but definitely doable - you'd just need to cut off the axe head, use a pin vise (hobby drill bit) to drill a hole into the end of the shaft and insert a pin (bit of paperclip or wire) into the end, and then find a mordenkrad head you like and drill a matching hole in the bottom of it and glue it onto the pin in the shaft. Reaper sells weapons packs, and you can buy individual weapon sprues from the Boneyard (their "bits" catalog).
If you do a search in the Reaper Figure Finder, for the keywords barbarian, axe and or hammer, you should get a fairly decent list of minis that would work for a goliath with a mordenkrad.
A better choice than Uglunuk might be Thelgar Halfblood or Goldar... Both are a bit on the large side for a medium character, and while Thelgar also comes in multiple pieces (his hands are attached to the axe, which is a separate piece) Goldar is a one-piece cast. (Gorak the Ravager might also be another option, but again, it's a multiple-piece casting...)
On a general note, unless you have some sort of physical disability it's ridiculously easy to paint your mini yourself to a higher quality than the paintjobs on the official DDM minis.
Painting it yourself (i.e., the cost of starting materials) will almost definitely be cheaper than finding someone to paint it for you, since anyone worth hiring to paint it will charge accordingly. Unless, of course, you find a friend or acquantance to do it for you and they give you a "friend" price.
Converting the axe to a hammer can also be done by those people.
Painting it yourself seems intimidating, but you can actually get a mini that looks good with little to no actual skill by using a method called "dipping", where you paint a mini in flat, basic colors (like a D&D prepainted mini), and then dip it in floor varnish (you can achieve a similar, cheaper effect, with special washes produced by miniature companies). Here's an example; www.lounge.belloflostsouls.net/showthrea...
By the way, good choice with Uglunuk. I painted one up for my friend's goliath, and it really makes you feel like you're playing a goliath when you put that on the board.