It appears to be an owner's arrangement of parts specifically for work with would require such jewelling chucks.
I should be not too difficult to find other 6 mm collets that would fit the lathe. Measure carefully all the dimensions, including the thread diameter and pitch and compare with the table in De Carle's book. In this way, you may find a matching brand.
I am not sure, but I think beds with partial flat are meant to turn the lathe into a simple drill by mounting the bed upright in the foot, after removing the clamp for the headstock. I have one of those and used it as the basis for my micro-milling machine. However, for many brands of Geneva lathes, the stem on the clamp has only 18 mm, rather than the 20 mm as for the bed. So this conversion does not work for all brands.