While a near as perfect exact make or model nomenclature would narrow or eliminate any chance of uncertainty...
Numrich arms
Jack first
Triple K
Possibly brownells but that's a bit of an iffy stretch
Those are the places / companies / catalogs / website locations I would try first to locate an OEM or reproduction replacement magazine.
I am going to hazard a guess you don't have a single magazine that fits the gun or we would see pics of the detached Mag or a well done carefully line drawing trace outline in black marker on white paper that might help compare it with ones used on other models that might fit across a lineup of several variants.
Having exhausted these resources or explored these options with no joy I would check out online auction sights of prominence or seek out a forum specific to this company and seek more narrowly focused expert aficionados responses.
The largest online seller of new and used items of all types might supply an example but is not exactly gun friendly.
But my best hope is that one of the knowledgeable fine folks here has your exact answer before you need to follow the route my advice proposes.
Mike