Ok so what i've found out is that many people have the same problem finding content on psn store when their psn account has a different region than their disk of mw3.
the psn store will show u only content for the region of your psn account, if ur account has US region it will only show u content from US. if ur region is germany then store will only show u content in germany.
Every country has its policies and restrictions and u won't find the same content for all countries.
What you can do is find the region code on the side of your disk and google it to see what region it says it is. You then create a new account and choose the region u found on google and with that account u access store and download the same region code from your game's case.
Install it once downloaded then switch to your other account and it should work.
I'm not 100% positive about this but its worth a try.
If it doesn't just delete the account u created.
