My Spiller & Burr is a kit gun that I purchased from Dixie a couple of years ago. It is made by Pietta. As Doc points out, since yours has serial numbers it probably is not a kit gun. I doubt it is a Pietta based on absense of the notorious "Pietta Billboard" on the right side of barrell. Mine has it and nothing else at all besides the BP warning on other side. The grips on yours seem much to nice to come from a Pietta kit also. I could be wrong, perhaps it is a Pietta manufactured before their advertising dept. went crazy.
You've got the names of where to get parts. In a pinch you can use Remington 1858 Army parts with minor modifications. You got an excellent buy at $160, kits are generally closer to $200 and finished S&B closeer to $250. You will really enjoy shooting the S&B.