1" air hammer retainer diameter?

[72lb4x4]

I have a US made air hammer that uses an apparently strange 1" diameter retainer spring. A digital caliper on the ID of the beehive spring shows .995." The smallest diameter of the "thread" of where the retainer goes is 1.02."

The tool has Air Inc. and model DV-612 stamped into it. It uses .401" tools. No luck finding the company or a retainer that fits on the internet or actual stores.

Any idea where I can get retainer springs or a quick change retainer? The retainer size was apparently standardized at some point and the standard is something bigger than one inch.

I hate to toss it since it works and is in nice shape...