[LargeFormat] mercury batteries

[Philip J. McCourt]

Does anyone know if there is a good  replacement for mercury px640 
batteries that were used in pentax spot meters. It is illegal to import 
them in the States nowadays. Wein makes a zinc air battery to replace 
the px625's and the px13's, but I can't seem to find one for the 640. B& 
H sells an alkaline 640, but the higher voltage would throw off the 
meter reading.

Has anyone had any luck dealing with this problem?

Phil McCourt