GreenManGaming

I don't know. When I bought FM13 for my friend I had to make another account. But you can use the same pay card.

It's limited to one copy per account.

They most certainly do have Killing Floor, and it's 75% off to boot!

As long as it's one copy per DLC or game per account :)

Also, they have a 20% off discount code but it is only useable on one item per purchase so if you wanted to save yourself a few pennies you're better doing seperate transactions.
20% off - GMG20-P4DLK-FKYRS

don't worry too much about it being out of stock, it says the deal lasts until monday. just keep checking frequently and most of the time they add more keys. sin mora went out of stock for me during a really great sale, but in a day or so they got more keys and continued the sale.

p.s. you wrote "buy few copies" and like teejax mentioned, you can only buy OnE copy of any game on a single account, at greenmangaming. it sucks because I've wanted to buy something for myself, and one for a friend (or to giveaway), but could not!