there's no way to go gen1/2 to gen 3+
gen3 ROM (with the save file named exactly the same but with the .sav extension) can be loaded by desmume as a GBA pak. You can use the pal park feature of a Platinum ROM.
To deliver it to your cartridge, you can use DeSmuME wifi, Fake GTS, or save editing (adding the PKM with a save editor).
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alternatively, you can use IR-GTS to transfer 3GPKM files directly to a retail gen4 game if you use the fake gts method.