Chuck,
I've uploaded a photo of the boom end fitting to Tern's album. I think this is the part you need replaced. If you don't have access to material and a shop to drill something out as Peter has suggested there are a couple of other alternatives.
I can remove mine and have it duplicated by a machine shop here, might be a bit pricey but I can get an estimate and let you know before authorizing the work.
If you would be satisfied with a bit of plate or flat stock drilled out as Peter suggests then I should be able to put that together, I may even have some material in the shop. You would then be able to have a proper one made while you are in Port Townsand, where you would have more control over the work.
Happy to do this if it will help.
At one time, when I had the end off the boom, I installed a bail close to the end fitting. It provides an attachment for the preventer but it was also my thought that I would have a bit of redundancy for the main sheet attachment, although I was thinking it would be the shaft/bolt part that might fail since it is hidden from view and difficult to inspect.
Craig