Most larger PT clinics have a variety of electric stim machines. Or chiro as mentioned.
TENS, IF stim and other kinds call around an ask, and ask which type seems to work best for PN.
You might ask about low level laser/soft laser for PN also..

But there are many medical devices for sale on Amazon and other medical product sites.. You can compare prices and read reviews on Amazon, other medical product sites don't have as many reviews...

I got my digital IF stim on Amazon for under 100.00.

I will suggest digital settings as the analog dials can be very touchy and easy to jolt yourself accidentally. I also have an analog dial EMS stim, that's how I know..