It seems there are a couple of places where black pudding can be purchased online in the US:
The only thing I can say is “Ecky Thump”.
You can have a proper breakfast! Actually, both stores sell the fixings of proper bacon, bangers, and black pudding to make a proper English (or Irish) breakfast! You can use the version I mentioned here.
I will update this if anyone has any other sellers in other parts of the US they send me.