Quick-release pins have already been mentioned. A local race-car or light-aircraft shop may stock a few of these.
There are also Cleco fasteners. These get used to hold together sheet metal parts that you're about to rivet together; the "nose" of the pin goes through a hole in both sheets and expands to hold them together. Picture of some in use:
The "classic" Clecos need a special pair of pliers to take on and off, but there is also a kind that works with a thumbscrew. One supplier:
Suggestion: For answers to future questions in a similar vein, obtain and read this book:
Matt Roberds