As for Squadron's site; it is kind of counter-intuitive. It took me some fifteen seconds to notice the big blue bar with the "Click here to enter our Online Hobby Shop" sign :P. It only yields 10 results if I search for hellcat in 1/32 scale, though, so you might want to check other shops.
You could also check
if you don't mind ordering from over-seas. They might have what you're looking for.
To my knowledge no one makes a set of wingfolds for the Hasegawa 1/32 Hellcat...and you're right - most folks scratch build their own vac-forming tables. I haven't built one, but from what I've seen, it doesn't look that difficult. And that's probably why a manufactuer hasn't produced one.
I have done it both ways - I've chosen kits just because I saw a set of etch I liked, and I've bought kits and set them aside until an etch set becomes available because I refuse to build a kit without using etched parts. I haven't used much aftermarket resin in a while, but I think that's about to change - the Zacto-Models parts for the 1/32 Trumpeter Su-27 are a must buy...
When it comes to aftermarket parts you pretty much have do your homework and then buy them where you find them...and some don't stay in production for very long. In the case of Zacto-Models you have to go direct to the maker, and there are also a few others I can think of that are like that. Sure sources I use for accessories are: Squadron (whom actually do a nice job of listing available accessories in thier search engine), Roll Models, and Meteor Productions.