I believe peruano sold me an oldschool chrome gas cap. It doesn't lock, but works well and looks nice. He might still have some.
For an ignition, ebay is handy. This link shows the results I just found. Some decent prices in there, but doesn't look like any amazing buys.
Good luck with it.
EDIT: This is just a guess, but I'd imagine any bike's ignition could be wired up to work. Mounting it might be different though.