Spyder
The main reason for backing a bow is that you can use "second string" wood for the core. Bamboo is a great backing, with bamboo you can almost make a bow out of "peanut butter"... Another backing that has a lot of elasticity is Black Cherry bark.
The closest Osage stand is about 35 mi8les from her it was on an abandoned piece of property not far from the Columbia River, but the last time I was there was in 1998. No idea if it is even still there. Another plentiful wood around here is Russian Olive and I have never found any reference to using that for anything.
There are some really nice stands of Vine Maple up in the national forest, about another 2000 ft in elevation, pretty high since I am at 3600 ft. I looked over my Mt. Ash, but it is all very crooked. The Vine Maple looks like the best choice, for me.
I also have quite a bit of Alder, that is probably the last resort. Back when I lived on the farm in NY, we had White and Red Oak, Beech, Hickory, Hophornbeam, a Blue Beech, we called Ironwood. And a lot of nice clear Locust.
I need to take a day and drop down on the river and see what is growing down there. Or go further up, there are some stands of Yew, that are not as twisted as the stuff that grows in my ravine.
I have to go quite a ways to find a lumber supply place that carries hardwood, for a board bow...