Try Amazon & Ebay, perhaps. West Marine is another possibility. Also, look at various RV accessories web sites.
West Marine has a decent selection of LED lights and various electrical gadgets, albeit a tad pricey. There is a West Marine retail store near by me so that compensates for the prices somewhat, just for the convienance.
I’m going to CLC tomorrow to pick up my galley kit, I’ll look / ask about the gasket material.