Wow! that thing is pricey...
Seems a lot of Gates belts are proprietary and cant be found in other brands - so I was curious and googled that # and was getting some other hits with pricey quotes, but after reading thru several I hit on this site and it wasnt too bad at $81...
http://www.vbelts4less.com/2530V934--VARIABLE-SPEED-BELT_p_24779.html
You might try McMaster Carr as they are noted for having many parts like belts and especially hydraulic packing seals for Clausing lathes you can call their customer care department as they are quite friendly (404) 346-7000, I have a 1500 and fortunately a great Clausing dealer here in Dallas, Texas.
Good Luck,
Ray