an alternative option, find a neon glass bender and tell him which voltarc tubing to use. Shouldn't be all that difficult to reproduce the tube, If what remains of Arista deems it too small of a market, then somebody there should be able to tell you what tube to use, and what gas mix they used, though it wouldn't be hard for a glass bender to determine that from seeing a working head.
If it really concerns you, before your tube breaks or goes kaput, locate one and have one bent up. If you do go this route, please let us know what tubing the glass bender found worked best (there's only a few suppliers of coated tubes anymore, Voltarc being one of them, so it should be easy)