Well, I lost the gas cap...

I would not be riding that with out a secured gas cap. Drop it and you will be spending more than $700 on replacing all your gear and maybe a hospital stay in the burn ward.
 
1. Rekey what? They don't even have a part number for the cap alone so there's nothing to buy to rekey.
2. I'm on an R3, my 2nd one in fact so im no noob, but if I would have gone down on the one day I chose to ride this way vs the other 3 when I didnt know the cap was gone and had nothing there, the missing gas cap would quickly become very irrelevant to a much more serious issue, wouldn't you agree? Thanks for your concern. The new amazon cap comes today.
 
110% this
 
It's that the same screw in one for the Bonneville and other models? I have the union jack one in my ebay watchlist.
I would go this route...
 
It's that the same screw in one for the Bonneville and other models? I have the union jack one in my ebay watchlist.
Probably, the bottom/neck part screws into the tank and the cap bolts onto the neck. Different manufacturers mount the lid differently, but basically the same concept
 
but they are not selling that single part at all. thats the issue.
Yes so buy a used one and have it rekeyed if you can find one. Or an aftermarket like others have said.
Depending on where you are, it might be illegal to ride with out a lockable fuel cap... Or at least one without a latch. It's like I said a serous safety issue.
Illegal meaning not road safe or "dot" approved for on road use.
Just food for thought