Does anyone have a source for the sliding window track
guides/plugs?  Or a couple of pairs I can buy?

Or can someone recommend a good workaround?

If not, I wonder whether we could set up a group buy and have them
fabricated?  I have no idea how hard or expensive that'd be.

My '84 camper's sliding windows don't latch properly with the guides
missing.  I mean, they stay closed while driving, but anyone can push
them open from the outside.