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:
formatting link
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:
formatting link
You might also find these at a local welding or sheet-metal supply house.
Suggestion: For answers to future questions in a similar vein, obtain and read this book:
formatting link
Smith was a race car engineer, so that's the main application area the book discusses, but the bits and pieces he discusses are handy in many areas. This book is an expanded version of some of the chapters in at least one of his earlier books, "Engineer to Win". Unfortunately it seems to have gone out of print and now commands a silly price, but if you can find it at a used bookstore or something, it's worth it.
Matt Roberds