Now that I know the name of it, I was able to do an internet search and there were a few companies who sell them. Here's what it looks like if anyone else is interested. I hope this link hooks up to the right page - it should show the tool as available through spartantools.com...
Several years ago I was at a vehicle assembly plant on assignment for a few months. An engineer who had spent time in Japan had a small pocket scale that was specifically designed for reading gaps, like in doors, decklids and anyplace else on the body.
This particular gap measurement tool...