If you're looking for a bench PSU start looking for "bipolar power supply/amplifiers". There are a number of reputable suppliers out there. This is, essentially, a laboratory grade power amplifier. The difference from just using an audio power amp is stability into loads that would upset an audio power amp, in some cases higher bandwidth and of course caring about specifications that are meaningless to power amp designers like line regulation. Secondhand ones are rare, I know because I keep my eyes open for them.
if you're looking for something to build in to something else in the sense of "off the shelf power supply" you're probably out of luck unless you're looking at a big enough order that you can say "Hey, TDK? Design and build these for me".