My understanding is that there are some sort of codes regulating the kind of connections that can be used for propane...
...but, if it wuz me, I'd just go to any local propane dealer or hardware store and buy a replacement hose for a propane bar-b-que. It will be a 1/4 inch ID hose, and one end will fit a propane tank. Cut off the other end and connect it to what you have with a 1/4 inch hose barb to 1/4 inch hose barb fitting that you can find at most hardware stores, or any agricultural sprayer supply place. Obviously, use hose clamps on both sides of the hose barb fitting.
I don't think that's gonna be perfectly legal according to the prevailing codes, but it'll at least be safe if the connection is outdoors. Propane is heavier than air, so propane can accumulate in a low area (like propane leaking from a propane powered taxi cab in an underground parking garage) and cause an explosion. As long as you're aware of that, and take reasonable steps to avoid propane accumulation in any low areas, you should be OK.
