If you can't stop the leak just by cleaning the seal (the one under the dust seal) with spray solvent/compressed air and perhaps the "film method", I certainly would not worry about the bushings or cartridges. They'll be fine!
Springs are worth changing if your sag measurement is too great. If you weigh upwards, or over, 200 pounds, re-spec'ing the springs is cheap and easy. Traxxion Dynamics spec'd mine and the spacers they provided were perfect the first time.
If you need the actual seals, MotoInternational is probably pretty close shipping for you and has a big stock of parts, as does Harper's.
Fork oil is a many splendored thing with lots of opinions on weight and fill volume. Easy stuff there with a few choices to make. The only "special tool" is to measure the gap down to the fork level. Sure, you can buy a fancy one, or just make one: