You didn't mention where you live, if osage grows in your area you can find a way to get some. I cut most of my osage in front of a bulldozer after asking the people clearing land if I could have it. I have seen a downed osage tree and contacted the city office to see if I could salvage it. I know if I put an ad in the local swap and shop paper stating that I wanted to buy standing osage trees I would be swamped with offers, most people hate these trees. Sometimes you have to get creative to acquire osage.
If you don't have the necessary equipment for cutting trees, buying is your only option.
If it is not in your area eBay is covered up with staves, the cheaper stuff is green, you do have to know your osage to separate the good from the questionable, your bow making skill lever will dictate what you can work and what you need to avoid.
I got this tree just by contacting the city road department and asking if I could salvage it.