There isn't one.
You must contact the maker.
Weihrauch, which was a German company specialising in high quality airguns and subcalibre firearms. Their approach with the Arminius line of pistols was a bit different, however.
The Arminius HW38 was mostly likely manufactured by Weihrauch, a German firearms company known for producing the Arminius line of revolvers. However, the exact manufacturer may vary depending on the specific model and time period it was produced.
Lorcin manufactured them. They are now out of business.
U.S. Repeating Arms Company
The Beretta Firearms Corp. manufactures out of Italy.
Glock. They are the manufacturer of firearms with their name.
Jacobus Arminius died in 1609.
Arminius Hotel was created in 1904.
SMS Arminius ended in 1875.
If it is in good condition and still fires, in today's market you would be offered about $100 to $150. Unfortunately, Arminius' aren't worth much. If it were mine, I would hold on to it for the simple fact that it is a working firearm. You won't get very much on a trade in or selling value with Arminius firearms.