"Mann" was one of the smaller German pistol makers, and I believe they went out of business during the inter-war years. Their pistols are not commonly seen in the US, though there are a few.
They were best known for making Vesttaschen Pistole (vest pocket pistols). I knew a fellow a few years ago who had one in 6.35mm (.25acp).
Your Mann in 7.35mm Browning is chambered for that round, known in the US as the .32ACP. Ammo is common. A 71gr FMJ is the usual load. There are now, some JHP loads, BUT I have no idea if they would chamber and cycle in a pre-WWII pocket pistol.
Do not use any kind of "hot" load, the small, blowback guns do not tolerate ammo outside their design parameters well, if at all.