I don't own one, but I've heard great things about SwissMicros calculators (https://www.swissmicros.com/products) from users of HP calculators. The SwissMicros lineup is very similar to HP's 1980s calculator lineup.
Also, the HP 12c financial calculator and the HP 35S scientific calculator are still being sold by HP.
oh shoot, I missed this comment elsewhere in the thread -- just want to say I got their HP15C equivalent years ago and it's high quality.
The HP Prime does have an RPN mode. I bought it recently, for that very feature, when my HP48 died. The keyboard of the HP Prime isn't really optimized for it (some trivial operations on the stack require key combinations, while on the HP48 there were physical keys for them), but it's acceptable.
A 35s and 50g got me through my engineering degree, I'm sure they'll still work fine.
I have the Droid48 app on my android phone. Pretty nice but I actually never use it.