Rca Pfr100

I just picked up an RCA pfr100, and it still works great after a little tweaking. Does anyone know if it is possible to replace the crts if they fail, or if its possible toupgrade the crts. The TV is a rebadged hitachi manufactured in 1982, the lenses measure 6" across. any help is greatly appreciated, I am not sure if this is posted in the right place, so sorry in advance if its not.
thanx