LogFAQs > #967168497

Every single existing trade evolution could easily be made a non-trade evolution if Gamefreak really wanted to. It's not that hard.

For the ones that require trading while holding a specific item, just require leveling up while holding that item and maybe also make it so the Pokemon has to be above a certain level for early game balance reasons. For the ones that don't need an item at all and just need to be traded, just give it another evolution level like 10-15 levels above the previous one. For the specific situation of Karrablast and Shelmet, where they evolve when specifically traded for each other, make it so that they both evolve if they both gain a level within a short period of time (like 10 minutes of real time) while together in the party.