Ryan, not sure from your post if you are looking for IV/V multiday runs, or if you are looking for day runs to train on?
Assume you are looking for multiday runs.
Earthen Exposure: river guide
Earthen exposure has some good lists of 4, 4/5, etc multiday runs.
For class IV/V multidays... I would highly recommend the holy trinity of middle fork feather devils canyon, deer creek, mill creek. All close to each other in cali, and odds are one of the them will be running if you are in the area at the right time.
I've done deer and mill and both were like 3 days of bailey but better. True wilderness paddling.
Also check out south fork salmon or selway (more IV than IV/V).
Do some searched on the buzz... tons of great info on multiday stuff. Also, earthen exposure is the single best multiday prep site I have found.