Kelly, any kind of laquer, varnish, polyurethane, ect. that was ever used to coat or finish wood will work. It doesn't have to be new stuff either. As long as it's still pliable enough to spread evenly on the stave, it doesn't matter if it takes 2 days to dry either.
I've got some old Helmsmann poly that I've been trying to use up and it's thick, dark, takes forever to dry but it works.
I wouldn't waste your TBIII and I don't think it's all that good as a sealer anyway. I've heard other guys say they used wood glue as a sealer and still got checking.
Surely they have some old varnish or something laying around over there somewhere? Even paint would be better than nothing at all, but I'd be afraid it would penetrate the wood and discolor it? Not sure, we need a few other old hands at this to step in here and offer a little advice.