Trigger, flintlocks and squirrel hunting are good things for sure. If you're serious about both here is some options.
Kibler Colonial comes in .50. .54, and .58 caliber. All calibers come in Smoothbore and rifled. A .50 Smoothbore might suite you.
He also offers the Fowler, now these come in 20ga and 16ga. Not a small bore but an option. You could also buy yourself a .32, or a .36 caliber flintlock and send it to Bobby Hoyt and he bore it out to a .410 Smoothbore.
I know you stated that yeah won't buy a Traditions anything, but I have to say their Crockett rifles are a great little gun. Plenty of folks on this thread can verify this. I spoke to Bobby Hoyt and said he can bore it out to a .410 Smoothbore. The Crockett is percussion though.
Food for thought.