Where Do I Buy A Power Supply For A PS4 Pro?

PS4 pro is a rather new console. Just to verify, you have ruled out the possibility of a defective power cable and outlet / surge protector? You might be able to find one on ebay or even a unit that has a defective HD or any other component rather that the power supply you are after.

That being said does your console still have a valid warranty standing? If so that may be the best way to expedite repair as the cost should be little if any. If not you can try your search engine for PS4 pro console parts and see if perhaps there is a company online that might have some part you can purchase. Also if you have no warranty and must replace it yourself, you can try local for sale sites like a Craigslist or such and see if you can find a donor console to cannibalize. Lastly you could try a PS4 powers up ply though that may be drastically different due to the new 4k Def support and the introduction of VR. Sizing and input / output specs may differ enough to cause damage so that would be your least best option.