I was there in nov of 08. Sun Kosi should be doable for just about anyone with reasonably good river skills, class 3 with one or two class IV's. The logistics is the biggest pain, I didn't do any of that. If you want something that is more class IV look into the Karnali. I would talk to Andy at Shiva Outdoors Home Page - BoatHouse Nepal
. He put together a raft supported kayak trip for a group of people there and my impression was he rented all the equipment from somewhere and pulled in some guides/cooks that he works with on a regular basis. There is a guide book Whitewater Nepal that I got on Amazon. From what I saw do not expect to be able to find "normal" equipment like cam straps, dry boxs, coolers etc. Expect to use rope for rigging and barrels as dry boxes and not really being able to keep "cold" food. If you just want to go on a commercial trip there are tons of options, I would suggest rafting in nepal, kayaking in himayalan rivers, Ultimate Descents Nepal - hidden fortress trek, canyoning, mountain biking, paragliding, hiking and more
as being the oldest most professional locally owned option.