The Deschutes River, the Fall River and the Metolius River are all in that area. Don't know what is open this time of year. There may be a fly shop or two in Bend, but if not, there are a couple in Sun River. They can point you in the right direction.
I agree those are definitely the big three in the area. The Fall River just had a fish kill either last summer or the previous due to pinpoint accuracy on behalf of the Forest Service with their fire retardant in the effort to put out a recent fire. So, it might be worth your time to focus on the other two river systems.