Unfortunately, the TTB system uses reverse-cut gears, which eliminates maybe 2/3 of potential sources for these. And, they're a popular gearing with the off-road crowd, so they get snapped up pretty quickly when they become available.
You may need to wait and watch the classifieds for several weeks in order to get a set inexpensively, or you can order them new from multiple places, like LMCTruck, RockAuto, or any good transmission supplier.