I just checked CheaperThanDirt.com, out of curiosity, to check on 9mm ammo availability since it is very difficult to find elsewhere. I say out of curiosity because I refuse to make purchases from them; I stopped being a customer of theirs months ago and you will soon see why. They have a decent variety of 9mm parabellum available. What they have runs from average quality ammo to cheap (note, I did not say inexpensive) Russian steel cased ammo but all what I think are exorbitant prices.
For example: They are offering a 100 (one hundred) round box of 9mm TulAmmo (a Russian brand of cheap, or should be cheap, steel cased ammo) for $139.59 plus shipping, see:
Ammo of that quality probably was going for about $10 to $12 per box, of 50 rounds, 6 months or so ago (at other sites). As if the current selling price at CTD is not bad enough, consider this: They are offering the same ammo in a 50 round box for $59.59 which is less than half the cost of the 100 round box, see: http://www.cheaperthandirt.com/product/AMM-4700.
Amazingly, it is $20.49 cheaper to buy two boxes of 50 rounds each instead of one box of 100 rounds. Usually, you would pay the same per round, for a purchase of 50 or 100 rounds of ammunition or maybe a bit less for the higher quantity of ammo. Paying more per round for a larger order was and is virtually unheard of except, so it seems, at CheaperThanDirt. I don't know who figures out their pricing but I would love to meet the responsible party and tell that person what I think of their prices as well as of their policy of listing their prices as: "Our Low Price". The price for the ammo in question is ridiculous, especially when you can get better ammo at a less expensive price elsewhere but I guess some moron will CheaperThanDirt what they are asking for it.
If you do need ammunition and cannot find it, you may want to try visiting http://gunbot.net where, as I write, you can get what I think is a much better brand of brass cased Aguila 9mm ammo at .72 cents per round instead of the $1.3959 asked by CheaperThanDirt for the TulAmmo. No, .72 cents per round is not inexpensive but it is about the going price for brass cased, FMJ, 9mm ammo nowadays and it is one heck of better price as compared to the other prices, for steel cased ammo, that I just mentioned.
GunBot.net lists ammunition in several calibers, with prices, from different merchants, with links to the merchants. You can sort the lists by caliber, then by price or most recently posted, and by what is currently in stock. The calibers which they list are:
[.223/5.56| 7.62x39 | 22lr | 9mm | .308/7.62x51 | .45 ACP | .300 AAC & Whisper | .40 S&W | 5.45x39 | .380 Auto | 5.7x28 | 10mm | 30-06 | 6.8 SPC | .357 Magnum | .38 Special | 357 Sig | 22 WMR | 17 HMR | 9x18 Mak | 44 Mag | 32 Auto | 7.62x54R | 30-30 | 30 Carbine | 25 Auto | 44 Special | 45 LC ].
This is how they describe their site: "Near realtime tracking of who has ammo in stock." As I was writing this, going back and forth to their site to copy the links and such, the list I had on screen, for .223/5.56 ammo (which is the screen the site opens with) was updated at least twice.
All the best,