Where to get "positive" or offset seals?

Hi guys,
I am replacing pistons and cam and would like to eliminate some small oil/ATF leaks that still existed after the engine and tranny rebuild two years ago.  I've read that I should be able to get front/rear seals for both the engine and tranny that are "positive" (meaning they have a spring or similar device inside the seal that forces it against the shaft being sealed) or seals where the lip is offset from it's normal location, so if any groove made by the old seal, the new seal would not line up with the groove.

Any idea where to acquire such seals?  I can't even locate anything via Google...

Thanks!

Check here.

All metal-clad seals have small "garter" springs inside them...or at least they do when they are made. A lot of times, the spring gets knocked out when the seal is beat in. Some heavy wheel bearing grease, or Vaseline spread onto the spring from the back of the seal will usually hold it in.
Don't know of any "off-set" seals as you describe. Sometimes, you can position the seal in a different area, tho. And..if your harmonic balance does have a groove in it where the seal rides, there is a thin, stainless steel sleeve that you can press onto the balancer hub to restore it's dimensions.