TWRoO, check eBay, I've seen them there once in a while.
Also, if you live in NA, EB Games has used games, and I've seen that collection a couple times before...a used game store may have it...
LEFT4DEAD411.COM
Bet with disolitude: Left4Dead will have a higher Metacritic rating than Project Origin, 3 months after the second game's release. (hasn't been 3 months but it looks like I won :-p )