Jeff; Many lathe belts can be had from auto parts stores. In any medium or larger city you should be able to find an industrial parts supplier they can match the belt on the lathe. You should remove the belt from the lathe and take it with you. I believe that they come with a spare drive belt. Gates is a large manufacturer of belts.
At harbor freight, they sell one of those belts that are made up of a bunch of small links and you can adjust to the size you need. I heard they work rely good. They have them at woodcraft too, but they are a lot cheaper at harbor freight.
I would check with psi since they carry that brand of lathe they sould carry it or if you can find a part number on the belt or maybe in the manual you could do an on line search Amazon may carry it. I hope this helps
When my Jet 1642 lathe belt broke, I found some reasonably priced replacements at www.beltpalace.com . They carry every type belt you can think of. I ordered two so I now have a spare.
Amazon also carries J Belts (the small light duty multi-v that most lathes use) but to easily find them you need to use the part # - but that's pretty easy. Length*10 J #Ribs so my 28" 4 rib belt is "280J4" ... $6.37 @ Amazon.
NAPA didn't have the J belts in stock, they were going to take a day or 2 to get them. I can have it from Amazon just as fast.