Mountainbuzz is forum that is mostly utilized by western U.S./rocky mountain boaters. So, I don't imagine that you'll find too many takers here that could join you on the Middle Yough in July. (However, due to lack of options here this summer, you just might find someone headed east looking for water to run.
Try posting on BoaterTalk: whitewater kayaking, stand up paddling, whitewater canoeing, river rafting
It's mostly southeastern paddlers. But some mid-atlantic paddlers lurk on there as well.
Otherwise, try the TRPC out of Pittsburgh Three Rivers Paddling Club // Home
They are probably running a several organized trips on the Yough this summer.
Or check out Ohiopyle Whitewater Rafting and Biking vacations with Wilderness Voyageurs
for kayak lessons, gear, and general info and socializing at the Falls City Pub.
I'm sure you can find some paddling partners in Ohiopyle in July. It's a really popular place that time of year.
Six hours seems like a long time on the water for that run. I think it is only 10 miles or so. Have fun. It's a great stretch for learning to run whitewater. The Ohiopyle area has lots of options for developing your paddling skills.