Unless Remington changed more than just the name on EAA Baikal shotguns and rifles when they took over the importation of that product line, I would think that Colonial Arms would have just what you want. I have owned several EAA Baikal shotguns--currently use a 12 ga side by side for hunting and trapshooting. These all came with 3 choke tubes. I ordered an improved modified tube from Colonial and got it, within a couple of weeks, together with their catalog. I've not bought anything from them recently--and I hope they still exist as a company. They carried tubes for just about any shotgun made, in nearly every configuration. They even carry tooling for threading barrels. Given that the Russian guns that now carry the name "Spartan" nearly all came with choke tubes, I have to think that the tube for your shotgun barrel can be obtained from Colonial.
