For my Sharp book, I am also investigating possible links between Sharp and Heirinkan.
Both companies were based in Tokyo and started producing airguns around the same time (fifties).
Heirinkan seems to have gone out of business in the seventies.
I read in a Japanese article that it sold barrels to Sharp in the fifties, until Sharp developed its own barrel making technique.

My Heirinkan Model A is probably better made than my Sharps. However, it is not as nice to use.
Extremely accurate though, and my most efficient pumper in .177 caliber, producing 11.3 ft/lbs on 4 pumps (pumping effort is above my comfort zone from 5 pumps onwards).

Any Heirinkan info is welcome. Photos, serial numbers, experiences...

Many thanks,
Louis