find any electric motor service company--they will know what wires to couple to change speeds or voltage

I also have a 6x48 belt sander with 12 in disc (belt driven) but I don't use the disc anymore---too many times a slight change in where you are sanding will change the force direction and you'll lose your hold on whatever your trying to sand/grind. And the belt sands in a straight line vs circular for the disc--makes it easier to control finish of what ever your working on