maybe add some measurement ( inside outside ) of the tube and maybe there will be some that have other makes models that can compare spc's too
most common to add longer tubes will be rem 870-11/87
mossberg 500's
I don't know spec's off hand on them but places like Mid way and such that sell them might have spec's listed on web site to see if they match up for you, if not they will have the OEM of the brands they sell and I gather the makers web sites should have spec's or can be emailed and asked for them!
to see if you can convert one to work for you!
Briely Choke tube maker(
https://www.briley.com/c-240-choke-tubes.aspx ) is famous for making and adding screw in chokes for shotguns, I would expect they have the means to MAKE you a tube extension, might end up having to ship them your shotgun, so they can thread your gun and match up a tube for what ever spec's you need to have an extension made
springs can be had again from other tube extensions for other guns I would imagine, same gauge would be close enough to work on all like gauge guns, as long as you get lengths right, springs should work IMO
just some idea's off the top of my head for you to think on?