A few folk find it more profitable to disassemble and sell some things as parts only too.
Or they found a NYC train dirt cheap but want a SF shell, etc.. "John" has a SF shell for sale after pulling the shell and dropping/bashing/ loosing the chassis "to movers", theif, etc. etc.
There are plenty of adds for wheels and trucks alone too
NOTE:The repair aspect of TCA type collecting says a "real", and nice, but used part trumps a re-pop for grading any day.... if a repop is even being made. Some items don't have the luxury of present availability.