In the resort area (Platinum)You can fish with a super rod and find magikarp from levels 1-100 (thanks sumwun). Also in Pokemon Platinum, after completing some quests, you can go into the Snowpoint Temple and at the very bottom is a regigigas statue. Go up to it and press a and you will start a battle against a level 1 regigigas. This regigigas can be caught, so it could technically be counted as a wild Pokemon .
I hope this helps you in your future endeavors.
Source: experience and sumwun (I don't know who though)
