According to past researches, between 3646 & 6152's (excluding prototypes) the Marina Military purchased approx. 160-180 pieces. It is known that some 80 pieces were sunk at large of 'La Spezia ' in a concrete block, this because of radioactivity issues. (if you are thinking about it, know that those waters are guarded...LOL)
In 1943 some of the watches in stock at Panerai were requisitioned by the Germans (although they had been paid by the Marina Militare). Earlier, the Germans were given some of the 3646 as experiments 2-3 units. It is assumed that post-1943, the German Army managed to acquire some supply directly from Rolex thus explaining 'California' and 'No-Name' Dialed pieces.
It also known that in the 1950's some odd version of the 3646 were obtained directly from 'Orologeria Svizzera' which was then the Panerai family civilian business of watches. I am not too sure how many, but seems it was around 5-10 pieces of the 3646 model case.
It is my opinion that the above number could not be increased/speculated by more than 5% either way.