Sorry I don’t really have an answer to the question you’re asking. Hopefully someone knows a shop or online service as I’d like to know as well.
Have you opened yours or have any plans to repair it? I would think that might be easier at this point than sourcing a new one. They’re very easy to take apart, you’ll need some torx screwdrivers though if you don’t have any. Or you could take it to a local shop if there is one.
idk, just my two cents as I bought one a year ago or so online full of dust and dead cockroaches (accompanied by their shit everywhere). Some may recall the pics I post on gaf, lol. I would be more inclined to try to fix it first since you know yours is (hopefully) not infested. Unfortunately, I’ve found most og xbox’s are pretty beat up consoles by now, inside and out.
Also, what version is yours? Not all of them need the time capacitor removed (the 1.6’s won’t work with it removed).
 ~$40 for a new PSU. I ordered my drive belts from this seller (albeit via ebay)