well,
your best bet is ebay, but your better off buying an old engine and taking the shell off,  ... OR....
if there a train show in town, your netter off going there since you get decent prices, and you save yourself shipping and handling.
plus the people who sell at train shows are often very knowlegable
and might give you some nice pointers....and maybe a discount...

wow, awesome pictures

mm... maybe your power pack isint strong enough 
try using another powerpack