THE OSA NO LONGER OFFERS THE OPTICS KIT.

FOR INEXPENSIVE LENSES, TRY:

   AMERICAN SCIENCE AND SURPLUS   (request their mail-order catalog!)
   http://www.sciplus.com

They sell:
  Lens Assortment, small sizes
  Lens Assortment, medium sizes
  Lens Assortment, large sizes
  Bag of 30 lenses


ALSO TRY:

  EDMUND SCIENTIFIC
  http://www.edsci.com