Probably no such animal as for-real Sunfish plans. There are some kits and kit plans dating from the 1950s and 1960s. The sort of stuff you would see in old Popular Mechanicx magazines. Yahoo Group Sunfish Sailor has a list of web sites and some free plans. Every plan I have seen is for a plywood boat. Cedar strip would look cool. Might need to adapt from the plywood plans. It's going to be very heavy by comparison.
I am in the middle of building a sixteen foot, plywood row boat. If I were you, I would consider using okume marine plywood, with fiberglassed seams (known as stitch and glue). This building technique is much more suited to the hard chined sunfish than cedar strips. It would be lighter too. If you really want the beauty of cedar strips, maybe you could do the deck like that.