The online Bulletins and Mart and Highlights are currently unavailable due to a failure of a network piece of equipment. We are working to replace it and have the Online publications available as soon as possible. Thank you for your patience.
Another real possibility Dave, is that the collets were acquired over time from other jewelers estates. I know that's how my Dad got his assortment. It is quite rare to find a complete set of Levin or Boley collets. If you find it, the price will be very high.
It is a possibility that you may need to use two same size collets at once, say in both headstock and tailstock. I use two #50's when polishing balance pivots. One to hold a baloon chuck in the headstock and one to hold an eccentric in the tailstock to support the other lip of the polishing shovel.