Basically as of now it is impossible to evolve pokemon such as Onix, Slowpoke into Slowking, or Seadra since they require items that (as far as I know) aren't obtainable in Kanto. I mean we could just wait until those regions are available, but to me it would make sense to have them available in the Mart, only for a large fee.
For instance, you could buy the dragon scale required to evolve Seadra in the Celadon department store for, say 50000 pokemonies, or possibly even more.
As with every other suggestion on this board I'm sure this will have some objectors, so fire away.