Why don't you call the jetflex retailer and see if they have any mis-matched paint they would sell you at a good price?
Failing that, try the same thing with your local paint supplier of PPG or DuPont paints. One thing - I understand that the auto paints have more fillers so they don't run as easily. So if you want to simulate jetflex, you may want to thin the auto paint a bit extra.
Painting a few things before you really start painting is a *great* idea. I was too short-sighted to do that and ended up costing myself extra time and money fixing the results of my learning curve.