Ellingtonic,
I would get some thin brass shim stock sheets (probably 0.001 inch and thicker). Hobby shops usually have some. Wrap a piece of paper around the shaft and cut it to size. Use that for a template. Cut the shim with sharp sizers and curl the shim around something smaller than your motor shaft to get a close fit. Then put the shim on the motor and gently align the pulley. If its still loose use a thicker stock. If its too tight, trim some of the shim, or sand a flat piece of stock to make it thinner and recut to size. You should get a near perfect fit with some trial and error.
JTA