Ranger 30
Moyer Marine is a good source for new and used A4 parts for sure. There are some books written about the A4 specifically, but I don't have them in front of me so I cannot give you a title now, sorry. As far as sails are concerned, you can go to any sailmaker and they probably will have the I, P, J and E numbers on the boat and hence can build anything you want. One of my boats is a Ranger 30 as well, a bit newer than yours, but also have a Universal diesel instead of the Atomic 4. It is a great boat and sails very well.
Now that I think of it, Good Old Boat has published a good article or two about the Atomic 4 as well. I have a copy of the Ranger 30 brochure if you don't have one. I can attach it to another reply. I have attached a couple of photos.