I've got a vintage HP digital counter, model HP-5216A. It was working, right up until the moment that it fell and broke two of the tubes' glass envelopes.

I really don't know where to source Nixie tubes. I see a few people who are making clocks with them, but not selling individual parts.

It's apparently an HP-1970-0025, which is a rebranded Burroughs B-5560.

Don't imagine this is the right place to find them, but I'm hoping it's the right place to find someone to tell me the right place to find them.