Hi Varjag,
Well I am amazed too ... I will try to find info about it in several books and tell you about what I found.
The MAS38 was only produced in small numbers at the beginning of WWII, then the French Army used much US weapons and in 1949 the MAT49 were issued. At the beginning of the Indochina war MAS38 were used but even MP40 had been issued.
Gendarmerie is part of the French Army, are you absolutely sure they were gendarmes and not policemen from the CRS (compagnie régionale de sécurité) for example ?
The Gendarmerie have the classical French Army's small arms.
Nowadays they have the MAS G1 (Beretta 92F), the FAMAS and still several MAT49 ... They also still use several MAC50 pistol. In fact the MAC50 is better than the MASG1 because it is not a real Beretta 92F but a model locally made and they try to make economies on several pieces and in fact it is too delicate for a service handgun ... now they have to return to factory to improve them ... stupid ...
French Police long used some MAB model D pistol in 7.65x22 mm (called 7.65 mm Longue) but in the army at the beginning the SACM 1935S and 1935A as well as the MAS38 used this cartridge. Nowadays it is not really used anymore I think. The French Army rapidly used MAT49 SMGs as well as MAC50 and MAB P15 pistols (all in 9x19 mm).
I really don't know where the MAS38 you have seen come from

) But sure I believe you, that's not the question.
Is the 7.65 mm Longue still available ? ... mmmm I don't think it is anymore produced ... but several Police handguns used them so perhaps ... I will ask my closest armory ... I am not sure it is still fabricated for the civilian market. About the 7.65 mm Browning (7.65x17 mm or .32ACP) yes I am sure you still can buy it but for the 7.65 Longue I don't know. Personnaly I am member of the French shooter association and have several weapons in .22LR, .357 magnum and .45ACP but I will ask for the availability of the 7.65 mm Longue.
The MAS 38 you've seen are in my opinion some "surplus" weapons issued occasionnaly, not really officially in use but still kept with the existing ammunitions stocks I think.
I will try to learn more about it and I will tell you later ... really sorry not to have more accurate infos in fact.
regards,
David