UI hired a guide in Welches for a day at the Fly Shop there. It was nearly 20 years though, so I don't know if the shop or guide are still there.
On subsequent trips though I found my way around easily once I had the DeLorme Gazetteer for the state. The regs. book is very good in saying what streams have what regs. and species. I believe I have a book about Oregon fishing somewhere, but I know there are guidebooks out about fishing Oregon that are very good. There's at least 1 Barnes and Noble in Portland down by the river, that should have the books you'll need.
There's fishing in the Coast Range, The Cascades, and east in the desert.