If you're looking for umps for a rec program, especially weekdays, I used to ask umps (if I thought they were good) after weekend games/local tournaments/other local rec weekday games, where they were from and if they were interested in umping during the weekdays for our program. I built up a good little network, usually if that ump couldn't ump, they knew another ump or two who could, they were usually also pretty good. You may also want to try to call different area rec programs, but they may not want to share their list with you, it's a lot of work to build up. Also, asking young men/women in their early 20's/late teens is a solid idea, but you can't go much younger than 18 or 19, was always more trouble than it was worth, at least in my experience/program (but my community was excessively competitive for rec, so it could work). I tried the umps list on this site, it didn't work very well, but maybe things have changed? Good luck!