Aftermarket manifolds and heads pop up on Ebay once in a while but are in demand and getting a premium price these days. Kansas Kustoms can split your exhaust manifold to a dual outlet.
Good luck, I have pretty much given up aftermarket parts for the 226 myself my pockets just aren't that deep. In my own mind I just can't justify dumping that much money into a Flathead 6. For the price of that aftermarket equipment I could completly rebuild a SBC and install it. I'm keeping my eye open for a salvageable 8BA for my 51 down the road.
Check out my gallery, I just installed an S-10 5 speed on my 226 and I just love it.

Rod 51F1