No More Heroes: Heroes' Paradise

You will get a few T-shirts just by ranking up. You will have to buy or find the remaining T-shirts.07-58 and 100-137 (unlocked in NG+) are bought from AREA 51.
T-shirts 59-99 are found in dumpsters.

This map shows the respective dumpster locations, credits go to Gamer-seven for creating the map and BreadSkin for finding the map.

If you want to see what T-shirts you’ve gotten so far you can check your progress in your motel room under the “closet” option.