Butterfree
- either dual slot mode with FireRed or trade from HGSS
Venonat
- Route 229 (Poké Radar)
Yanma
- Great Marsh
I think trading for a Butterfree would be best; none of the other Pokemon that have this ability are fully evolved in Gen IV. But if you don't plan to use the Pokemon in battle, you can have it fainted and leading your party & the ability will still be active.
