I found a source for Blockleys in California and bought a pair http://www.lucasclassictires.com/19-400x19-Blockley-Racing-3-block-tread-BW-283p.htm

Then yesterday I was reading a magazine and saw a familiar tire. It is sold by Coker tires. A bit cheaper than the Blockley.

http://www.cokertire.com/400-19-excelsior-comp-h-blackwall-tire.html