Okay, I don't know much about Thompson BB's. There's one on my wife's bike, and I haven't messed with it.

How much of the BB do you need? As I understand it, the cups are pressed into the shell, as on an Ashtabula crank. Are those cups present?

I wonder if the cups are the same as the cups on a Strida BB. If so, then possibly a Strida BB (which has square tapers for cotterless arms) might work. If you don't know what I'm talking about, take a look at this post on the Strida Forum. As it happens, I have some Strida BB parts in my parts bin, because the freewheel crapped out on me, and they sent a whole new crank with BB.

Give me some measurements-- shell width, shell diameter; and tell me if those cups are there; and I'll check what I have. If a Strida spindle and cones etc would work, that would be a pretty neat solution.