Update - I just accidentally bumped into a solution to my umpire shortage. Called my assignor for high-school football to make sure he'd gotten my dues and I hadn't missed any emails (hadn't heard from him since the end of the season). In passing, I mention my empathy for his scheduling problems, as I'm now UIC for Softball in my area... and he eagerly volunteers. I have no idea if he's any good, but I know from working football with him that he CARES, and HUSTLES.
Hallelujah!
So if you're shorthanded in your area, apparently the solution is to go work football!