I've got a NOS Warn/Arctic Cat 2500lb winch in the box setting on one of my shelves in the garage as a back up just in case needed.
But anyplace you can buy Arctic Cat parts can get you what you need.
You need Part#0409-066
This is a good place to get it from, with the best price I could find on them.
2005 ATV 500 AUTOMATIC TRANSMISSION 4X4 FIS LE GREEN (A2005IBM4BUSM)
Assembly: WINCH ASSEMBLY
Solenoid (inc. 17-18) (SKU: 0409-066)1$56.96