Is the BFG Radial TA the only 14" tire available anymore? I'd like to keep my original wheels on my 67 RT but would prefer a decent handling tire if possible. Car has a FF stage 3 and Bilstein shocks and handles pretty good, but I'm sure that could be improved with tires.

I liked my Hankook Optimos; however, they don't make anything wider than a 205. You may need 15's and even that selection is slimming down.

14" tires are extremely limited in availability especially if one is looking for "performance handling"

With 14's I am thinking you are pretty much stuck with suppliers like Coker etc. UHH performance ?? Not likely.
BUT, HMM, Googling,
14 inch performance tires

netted several possibilities. Google is your FRIEND,

I have Cooper 225 70 14's on one of my cars and they are still available. Discount Tire sells them.

I have Cooper cobra 235/60/14 on the back of my dart and hankook 215s on the front. Again, discount tire.