There are a couple more South Fork of the American runs you likely haven't run:
Kyburz (haven't been on the upper part, but lower is 4- to 4), along with
Riverton to Peavine which is slightly easier.
Lobin on the North Fork of the Feather.
The best thing you could do is to find similarly skilled boaters that are familiar with the runs and more skilled boaters who still enjoy Class 4 boating. They'll ease you into things.
This site may also help. It lists a lot of runs by difficulty: The Tip of the Iceberg