I have gotten Osage off Mike in the past.
I did not buy the pre cut slats you speak of.
I bought Osage boards instead, @ $10.00 a board foot.
2 inches thick, varied width, 36 inches long or a tad longer. Depending on what he had.
Much cheaper than buying the pre cut slats...
But I have the tools to cut it down into slats and run it through the drum sander to make it into perfect slats.
That may be an option for you.