The newest version of PokéRNG has encounter slot support (double-click on a spread to list all possible encounter slots and their frames). I've finished an update for it that adds searching by encounter slots; this will be up within the next few hours.
BTW, to search for Pokéwalker frames using PokéRNG, set the year to 2000, and the minimum and maximum delays to 0 and 99. Remember that the Pokéwalker frame is the method 1 frame + 2. That way, you'll only get seeds that are possible on the Pokéwalker. See Wild Eep's guide for info on natures (my post is really just a collection of info; Wild Eep's is more of a guide).
BTW, to search for Pokéwalker frames using PokéRNG, set the year to 2000, and the minimum and maximum delays to 0 and 99. Remember that the Pokéwalker frame is the method 1 frame + 2. That way, you'll only get seeds that are possible on the Pokéwalker. See Wild Eep's guide for info on natures (my post is really just a collection of info; Wild Eep's is more of a guide).