You can get it at any marine store or paint & body supply store.
But you don't have a gelcoat issue. You have a bad clear coat issue and that is why it is peeling.
Now is the $400 to sand and reshoot the hood with clear? Shop around for a better price. Its just a hood and there is no base color only clear.
IMO 600 is to abrasive. I'd wet sand it first with 800 and then 1000. Then I would buff it with marine rubbing compound or automotive compound. If that restored the shine then I would would apply wax or sealant. That is how I take care of heavily oxidized older boat hulls. But they are made with better materials and have higher production standards.