As I understand it all the basic design is the same, but was tweaked for the Spotmatic to make it less vulnerable to shutter capping.
The problem may be with the search term. I think the H1a was sold as the S1a (or SV for the next model up, same basic design but with 1/1000 marking and a self timer) outside the USA. H is of course the initial of Honeywell, who imported them as "Honeywell Pentax" while everywhere else had them as "Asahi Pentax". If you try looking for an S1a or SV manual you may have more luck.
You are correct, the fact that the H prefix was used only in the US didn't occur to me.