Do you have a local sawmill,they usually have a planner
I see no address as to where you are at. If you were near Wimbeley, TX. I'd say come on over. I own a classic 1979 Craftsman belt driven plainer/joiner that is a classic wood eating machine, and could do the job in seconds.
I use a Wagner Safe t Planer in my drill press it is slow but not expensive and works fine for small projects you can find them on line google Wagner safe t planer there are several sites that sell them . you do need a drill press with a 1/2 in chuck :)
That's some really gorgeous spalted maple(?). Don't know how stable it is, but a thickness sander might be a better bet, especially if it has gotten very soft.