I did find a Zipline Bats eventually.
At Wal-Mart, of all places. The last place I really wanted to go. I'd have rather supported a comics store, but most of those in my area were only bothering with the Bats & Supes 2-packs. The plus is that I paid $1.25 less than I would have at TRU.
I also opted for the Bats/Nightwing 2-pack, because I really wanted the Nightwing figure. The Bats figure is a repainted Martial Arts Batman, which isn't a classic but is one of Mattel's better looking variants. I can live with it, and if I can't, I'll pass it on to my nephew.