Justy,...
doors get broken off recorders because people don't take care of their things, or being so small, maybe the Porta02 suffered an accidental pull off the table, onto the floor. You never know.
Tascam Parts dept can be reached at (323)727-4840, and they'll sell you any repair part that's in stock. Service from the parts dept reps is pretty good, and don't lose too much sleep over Tascam parts prices, because they're the only game in town for genuine Tascam parts.
Sure, you could be like The G/H, and try to fix it with a cigarrette case or something, ahah, or maybe a cassette case.
The replacement of the door may take some disassembly of the Porta02, but I'm not 100% sure about that. The part should be readily available from Tascam. Good luck.