I took advise from another thread on this site, and screwed a small screw into the space where the broken gear tooth was, then filed it to match the bevel and length of the other teeth. This at least bought me time to continue using the shredder until I find a gear to match-if that's possible. Gear is 3" diam, 29 exterior teeth, #390346 stamped on side.
gnalch (my post, my solution so far), December 2008