Mag Extension for Spartan SPR453?

I posted this on Biakal/Spartan but no responses yet so I thought I would try here.

Do you know if anyone makes a mag extension for Remington Spartan SPR453 or Baikal MP153?

Or if a mag extension for another shotgun would fit?

My last resort is to cut the exhisting cap and weld a tube on it and get a longer spring from Wolf Springs. Man it seems like alot of work to get a mag extension. However I wanted a gas operated autoloader and not a recoil operated autoloader.

Any help or suggestions would be greatly appreciated.

Thanks.

Dan