I don't believe this is even a cavalry saddle....rather it is an artillery model of the Mac as can be told by the "D"-ring on both the pommel and cantle of the saddle.
As to the CSA slot plate, these are readily available from any one of a number of "sutlers" on the reenactment scene. Originally, it would have been a number like 13 that would indicate the size of the saddle.
J