Welcome to the fun!
Maybe contact FrankenFrakenstuff here: he has an injection molding machine and makes side covers for LOTS of bikes like ours. I have a set on my 750K2, and their quality outstrips the OEM version by a stretch.
The latch: CMSNL is a good place to look: I'll check the K7 tank in my shed, but I think someone already got the latch from the lid. Sometimes I have seen just the door lid on eBay, too, with the latch. It opens with any short, straight blade: it's not a key lock, just a latch.