Amazon is a good source (example …
https://www.amazon.ca/Adhesive-Automoti ... 64&sr=8-28).
I find that unless you know exactly what you're after, RV dealers aren't a lot of help and other suppliers won't let you rummage through what they have while you "design" things on the spot in your head. For the small amount you might buy it's really not worth their time.
Although this is a bad time because of the virus, I've had good luck at flea markets such as the Barrie Auto Flea Market (Burl's Creek - June & September), The Ancaster Flea Market (Fairgrounds - April) and the Motor City CC Flea Market (International Centre - December).