Osage is difficult enough to make into a bow. I can't imagine why anyone would want to take the time to split out a stave to then turn into a ramrod. Hickory is much straighter grain, and easier to work. Hickory is widely available, and far more commonly used.
You don't say how long a ramrod you need, but that is going to make a difference. If you have ever hunted windbreaks, ( windrows in some places) put in during the Great Depression, these trees are almost always Osage Orange. The trees twist in the wind and the grain follows the twisting shown on the bark. I don't think I have seen an osage orange tree with bark that was straighter than about 30 inche, and that was probably on an inclined turn. Vertical bark is almost never found.
These are very hard woods on any kind of saw, and they get used as fire wood, more than anything else, when they are cut down. If you find a copy of BowHunter magazine, there is a many here in Central Illinois- Mystic Archers-- I believe, that sells Osage staves and teaches classes on bow making. He may not have anything you can use right now, but I am sure he would be willing to keep an eye out for you, to find you the length you will need for your Ramrod.
Most of the Osage trees I have seen all my life are in these wind breaks. Hickory grows everywhere, but seems to do particularly well growing up from the bottom of steep ravines. It is the ravine that protect these trees from the wind, so that you get a couple of dozen feet of straight grain and a ramrod straight trunk, very skinny, that support a few branches at the top that have leaves. I have seen 40 foot tall hickories that are barely 6 inches in diameter at head high. That and larger diameter hickory trees are where you want to be getting wood for ramrods.
If you live, or have any contacts in the midwest states of Arkansas, Missouri, Iowa, Kansas, Nebraska, Illinois, or Indiana, look for Sawmills. Then contact them to find out if they have any osage orange wood stacked in their yards. You sometimes see it being sold in 8 foot lengths for fench posts. It will be cheaper for you to buy a whole log and split it out yourself, rather than buying a split that someone else has to do for you. With even the best split, however, you may have to plan on doing your own straightening of the rod.