40K Mordian or Praetorian figures would be closest - you just need to cut off their hats and greenstuff your own, and maybe make the guns look more muskety.
That said, these are mail-order only, so it certainly wouldn't be cheap.
Another route to go would be to go online looking at historical mini makers - these would certainly be cheaper & require less conversion, but scale issues are likely to come up.
A third option is to convert the empire gunners by greenstuffing them new hats, etc. - I'm not familiar enough with the models to say how feasible that would be, however.
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