As mentioned: Wyrd, Foundry zombies and Deadlands are good sources.
Brigade Games Gaslight range has some weird wild west stuff too.
Also the horrorclix range has some good figures: a vampire in top hat with victim, a snake oil salesman with actual snake, ...
Crucible boogeymen (Ral Partha/Iron Wind Metals) fit in well too.
You might pick up a Perry ACW box of plastic to convert with your GW zombies. You can either zombifie the ACW figs or cut off heads/hats/weapons/equipment bits to put on your zombies.
I also converted some skeletal indians once by greenstuffing long hair, feathers, etc... on skeletal archers.