Need help finding shotgun choke

[RUGER]

Buddy bought a used shotgun and he needs to find one of the screw in chokes for it and hasn't had any luck.

Brand name is ATA, model is Diana.

12 gauge, 3 1/2" chamber, automatic.

I have looked everywhere and can't find squat.
Any help?

 

[TiminTN]

http://www.paciko.com/web/AtaE.htm

 

[buzzr46]

http://www.ataarms.com/

 

[Chaneylake]

if all else fails, contact Briley or Kolar i know they have web sites, they can make anything that a person wants, kinda expensive better than nothing if you can not find one on shelf somewhere