572B's are still made - people like RF parts have both "New Old Stock" and the
current Russian ones. Ameritron sells an amp with 572Bs in it (yuk!).
Go to Google and type in "572B" and you'll get dozens of hits.
I actually have my Dad's old FL2100B that hasn't been turned on in 20 years. If
you have a big variac and live close to Lafayette CA, let me know :-) Otherwise
I intend to eventually get the thing working again, but I'd like to unsolder
the caps and test them first.
Another possibility is to wire the thing for 220V and bring it up on 120.