You need to buy a selection of sandpapers, 220, 400, 600 and 1500 grit is what I used. After the final 1500 grit wash the forks down with soapy water, dry them well then coat with clear lacquer...I used 5 coats with a 15 minute drying period in between coats. They came out looking like new but it was bloody hard work, 3 hour per leg.
Make sure you do the sanding in one direction. I chose horizontally around the fork diameter. If you mix it up with vertical sanding it looks bad and makes it a lot longer process as you have to refinish the areas where you've gone against the grain so to speak.
The 220 grit will completely wipe out the pitting and you'll probably get a bit scared that you've done too much but don't worry as the finer grits clean it all up and you'll end up with a near mirror finish by the time you get to 1500 grit. It's important to lacquer afterwards as the weather can quickly fade the metal, enough coats will to a certain extent protect from stone chips also.