ive been starting up a witch-hunter character and have a few basic ideas of how I want to play it, but I'm looking for a few suggestions for more hardcoe RPers.

So far I've decided that I will not kill non-supernatural beings (instead use unarmed and RP that I'm just knocking them out), and then archery and silver sword for anything else. However magic users are fair game even if human/beast race.
This character hates magic used for evil and does not use it themselves either.

My problems are how to pursue a hunter career without using my own knowledge of the game to find enemies. I would rather have my character find the leads themself. Any ideas on RP suggestions?

FYI witch hunter is just a general name. This character just kills anything supernatural (think winchesters 馃槣)

Just a couple ideas -

Your inclination to use a bow is perfect. If you don't chase them, those mages tend to put up a ward, stand in place and sling spells. Standing still with a bright shining light in front of them makes them a perfect target for arrows and their wards do little to stop arrows. That leaves you to deal with the spells they sling at you as you shoot. The answer here is to load up on magic resistance to ensure that you are taking little damage from them as you shoot. As far as a race, not a big deal but Breton is a nice choice (magic resistance) and so is Bosmer (archery skill starting bonus).

As far as RPing how to get leads on evil magic users, consider joining the Companions but only doing the first quest or two for them so you remain very low in their pecking order. Then just pretend they recognize your skill as a mage hunter and give you jobs to go eliminate them. That is where your knowledge of the game can be worked in - as 'pretend radiant' Companion quests. Plus, Jorvaskr makes a great base - nice atmosphere and very centrally located.

If you'll choose the race based on the gameplay bonuses, definitely go for a breton. The difference between a virtually non existing edge at the start of the game and couple of extra skill increases more combined with permanent resistance to all magic is not even fairly comparable.

Another approach is to join the College and roleplay that you are a sort of College "fixer", whose job it is to go out and destroy evil magic-users and anything in their lairs.

You can get quests from Urag (he has several repeatable ones, which is perfect) and recover lost knowledge - protecting powerful books and scrolls from falling into the wrong hands. Sometimes these radiant quests may lead you to necromancers' hideouts, etc.

You could also RP that you have heard rumors of the Forsworn using forbidden elder magic, which you must stop. Visit Markarth and get bounties from the jarl and the innkeeper - those hardly ever seem to run out, and will keep you busy for a long time.

In other cities, the "asking for work" dialogue topic will usually get you bandit bounties, but at higher levels can get you giants or dragons. That's not terribly witchhuntery, so you might just avoid those.