Wanted, Dark-field Condenser

[georgetsmurf]

I am looking for a affordable dark-field condenser to fit my S series Nikon microscope. The mount diameter is 36.70mm (a bit of a strange size for a japanese product) but that is what it measures with a vernier. There are obviously brand new products around but even a Russian LOMO is several hundred dollars by the look of things. I recently missed out on a Nikon one on Ebay that jumped over $100 in the last few seconds of bidding. If anybody knows of anything, please let me know. The mount diameter is not critical as I can modify if necessary. The standard condenser on these microscopes is marked 1.30. alternatively, does anybody know if a standard condenser can be modified to darkfield as I do have a spare standard one.