Our local Ace stopped carrying PC-7 a few years ago. Online search indicates that Home Depot is an authorized distributor but I've never seen it in the local stores. IIRC in an old thread, Ldub posted some stores that also carry it.
BTW, PC-11 would work too. That's the marine versionbut it's a blue-ish white. I prefer the PC-7 though since it is the same color as the cladding (dark grey-ish, black sorta color) if you get sloppy & end up with some where it'll show.
BBTW, this stuff would also work good to fix cracked a hood insert.