The Fear Nothing English t-shirt can be found in lockers during the “Pachinko Model” mission.
The other version is a Fear Nothing Kanji shirt, white.
Note: The Fear Nothing shirts are in specific lockers. As lockers are random, you don’t always get the lockers containing them. Running back out and in will reset the locker randomization, so you can keep exiting until you get them.
The Fear Nothing English version in a locker on the right side.
Thank you Tally, Simondedalus and Vomher for the screenshots and details!