Wow... 21 teams! I was just thinking about how I don't like the idea of 8-team mixed leagues, because everyone has 22 studs on their roster. All 3 of my leagues are 10-team, NL-only, which seems to work pretty well. I wouldn't mind a 14-team NL-only or a 20-team mixed, though.
Anyway, Bako seems like he might be the best bet. Brian Schnieder might not be so bad either (recently Barrett's been getting some time at 1B, with Schnieder playing behind the plate). Other choices might include Vance Wilson (Piazza's backup, but, hey, he's done pretty well so far) and Robert Machado (he's been the best hitting Cubs catcher so far, and the Cubs are desperate for offense).
If it's a rotisserie league, consider starting a minor league or injured catcher, but check on your league's at-bats rules first. While other people get hurt by catchers batting .215 with 500 AB's, you'll laugh with your catcher batting .000 in 0 AB's.