Can 12AX7s and such still be ordered?

Yup. Tubes that are popular with musicians (for guitar amplifiers,
etc.) are still in production in a few factories (China and Russia,
mostly), and there's still an active trade in "new old stock" and
"used and tested" tubes of these types. The 12AX7/12AU7 family are
heavily used in guitar amps, and so remain available.

I recently lucked into finding a big batch of tubes of various sorts
at a garage/moving sale... got three boxes of used tubes, two
emission-type tube testers, and some manuals and tube-data guides, for
the "please take this away, I don't want to take it all to Arizona"
price of $4. A friend of mine glanced at them, and identified several
Telefunken 12AX7 tubes ("These are gold!"). I ended up selling a
batch of seven of them (tested good on his fancy tester) on eBay for
$145!

Sorta hated to let them go, but none of my audio gear is
glassFET-based and I figured that other people could make better use
of them than I.