Templates do not exist as far as I know. The reason is that there are as many different ways to build them as there are canvas makers. Even if you look at ONLY dodgers, there are tons of different ways ON THE SAME EXACT BOATS to make the frames, canvas and glazing.
That said, there may be vendor that the factory uses, but I would guess they would do more dodgers alone or dodgers with connected biminis, rather than full enclosures. The full enclosures are used in places pretty far away from Florida where that vendor is located, near the factory IIRC. Sorry, forgot their name, might be in Mainsheet magazine.
Almost very single Catalina size boat has its own owners association and usually a website. In your case c20.org. You could ask there.
Photos could be available if you do a Google search on Catalina 320 - I got tons of hits for boats for sale when I found the C320 association and their website on Google.
PS - often folks will ask about where to have canvas work done. Two answers: 1) mail order; 2) local. Local is almost always more expensive, but you have recourse if things don't fit and/or they need adjustment - because with canvas it almost always does.