Sliding screen door rollers

We just moved into an Eichler.  We're renting, but I am a general contrator and I have agreed to do some repairs in exchange for part of the rent.  First on the list are the screen doors which are in sad shape.  I particularly need new rollers for several of the doors.  Can anyone help with part numbers or possible replacement rollers that can supercede the original ones?  It doesn't look like the broken rollers can be replaced within the existing carrier, but perhaps it's possible.  Many thanks to anyone who can help.