I just stumbled across: russian ILD3 tubes, CRTs without deflection, choose yer phosphor color red or green or blue. Apparently these are from stadium-size color display (the pixels.) A couple of eBay sellers have them ~$10. Anode 7KV
Use as electron microscopes! (Or at least show off some electron optics for physics classroom.) I bet they can image their own cathode surface like this:
Also, EM84 eye-tubes are pretty cool. Under $5, buy handfuls for electron-beam kinetic sculptures, rectified 120VAC works ok for V+.