Charles, Please do take a moment and contact Ring Engineering and encourage them to provide Mac support. The more requests for it that they get, the sooner it will be developed. And perhaps they will have a suggestion for you.
Kevins suggestion of using Parallels is a good one. You can download and test the software before purchasing, so at least you can confirm the option.
Also, if parallels does not work, older laptops and PC's that do natively support RailPro are a dime a dozen. It might be possible to pick one up for the railroad room without much expense.