Hi Mark, if you have not already done so, I would joint the Yahoo Boxford users Group.
Not the easiest of sites to follow though. In there you will find charts showing all the specific gears you will need and their correct positioning. I have gone thru' the same exercise.
A few I bought from Tony at lathes.co.uk.
You can buy all from there but they are pricey. I think you will have to get the 127/135 from him as they come up very rarely on the Bay. You can get other odd ones off the Bay. Also try bedetools.com as they have quite a few. G and M tmachinery also have a few at film star prices.
When you know exactly which you want, put an add in the wanted column on here.
Malc