Have you tried the Mac parts dept?
Since they're still making the MC-275, I'd suspect they will still be using them. BTW, without looking, I believe you'll need a CL-90 - but I'd check with Mac first.
I had to replace the one in one of my MC-225s, when it literally fell apart as I was reworking the power supply.
As far as other suppliers, Mouser should have them - they're pretty standard parts. Also, Google the CL-90 and you'll get lots of hits with tables to the other CL series parts.
Hope that helps.
Cheers,
David