The best way to source a CRT is to get a "broken" unit which simply has bad caps or a bum analog board and is classified as "non-working" by someone who doesn't know the tricks of repair.

Remember to check the type of CRT in your Classic if you do replace it--Apple used two revisions in Classics. See the stickied thread in the compact forum for more information.

(To further elaborate--CRTs are tough to ship on their own but are far easier to get through the mail if there's a mount and case around them. I once sold a CRT to someone and gave it to him in a beat-up SE case to protect the CRT itself).