Those deringers were made by a number of companies, most out of business now although I'm sure you could find at least one company that still makes small guns like that.
Yours may be chambered in the 38 Special caliber but, and this is a big but, they really aren't all that safe. I had one similar to that for a while and got rid of it. At firest both barrels fired as they should but then one stopped working. The standard 38 spl wadcutter gave noticeable recoil and the gun was hard to hold on to. No accuracy to speak of. They are neat little things but are most likely best found in a safe or on a wall. If you want a deringer type handgun try one of the older High Standards if you can find one.
If that gun is as old or older than you are I would think of adding it to a non-working collection and be glad you don't have to depend on it. JMHO. Mikey.