Hey Alec,
Here are links to two services for distribution of self-produced music, one for iTunes and the other from Amazon. I am not a musician, but these both look like excellent services.
TuneCore (for iTunes)
Amazon CreateSpaceTuneCore will get your music on iTunes for what looks to me like a nominal fee. Amazon CreateSpace will manufacture physical CDs (and DVDs and books and who knows what else) for you whenever people buy them, and it also looks like you can get your music on the Amazon MP3 store.
You could also pay for professional duplication, but that seems less attractive to me for three reasons:
1) You incur an out-of-pocket expense of a few thousand dollars (depending of course on the size of your run),
2) You have to mess with warehousing (a bunch of boxes in your residence), order fulfillment, and customer support - what a mess!
3) Whenever you run out of stock, you need to order more prints.
Finally, you could just sell MP3 files direct on your web site. Peter Breinholt does this, and as a customer I think it's great and wish him well. You would get more money from these sales since Amazon/Apple wouldn't be taking their cut. You may or may not get as many sales this way, but it's probably worth doing just because you'd get more money from each sale.
Actually, you could do all three of those. Why not, eh?

Anyway, I know you didn't actually ask for this, but you did kind of beg the question. May you find these links useful in your quest to produce a soundtrack, which I'm probably going to buy (but not until after I beat the game, and I'm waiting for the Mac version. So, uh, take your time on releasing the soundtrack

).