Hello Marc,
I acquired several assortments of loose hole and cap jewels quite a while ago but do not remember the suppliers name. You may find assortments on ebay or can check with suppliers online. I use jewels from these assortments often and fit them by measuring the diameter of the jewel and the inside diameter of the whole or setting that it needs to go into. Of course the hole through the jewel is determined to be the correct size before hand.
Best of luck Marc and happy holidays to you.
Ian