Not sure if you're still looking for information, but I thought I'd chime in.
I'm living in San Jose now. I met up with a guy in the town of Peibeye, which has a III-IV section who is from Turrialba. Carlos speaks English, was a member of the CR national raft team, and grew up in the town. His brother lives that and runs one of the lodges on the Pacuare. He can definitely coordinate shuttles for you with local private drivers that have trucks to haul your gear. Or he might want to run the shuttle for you, depending on where it is. Super nice guy. If you still need info, PM me and I'll give you his #, you can reach him on Whatsapp.
Otherwise, the standard practice is to stay at the Hotel Interamericano and you'll usually have a few boaters to hook up with to run stuff in the area.