The new Ithaca manufacturers are taking a "slow but sure" method in ramping up for manufacture and distribution.
Their website says that they are not selling to distributors and dealers until their guns are 100% made of new parts that they themselves have manufactured, they don't intend to mix "new old stock" parts into these guns. I am not sure the previous Ithaca guys were as meticulous as the new manufacturers, but the new guys are basically mold makers, and mold tolerances make standard firearm tolerances look awfully big, and they seem to strike me as a persnickety bunch and perfectionists, which is okay by me.
I am not sure as how what parts are available on ebay is relevant. Probably not a lot of Deusenberg auto parts on there, either, but that wouldn't dissuade me from trading my Buick AND the Dodge for one.
In the end, a single load of shot from one shell passes through a specific choke and comes out only one barrel of that particular shotgun you have to your shoulder, so whether some place has 64 varieties of barrels and 132 choke tubes or none for your gun, it won't be a factor for that shot, because eventually you have to boil every choice down to one when it comes time to pull the trigger.
Somehow, the LAPD was able to muddle through with the Ithaca M37 in every squad car for close to 50 years as a "tactical" (whatever that means) shotgun, as well as some guys in Vietnam. Of course, none of these guys ever had to shoot in some sort of "tactical" shotgun course, they just shot bad guys, so they might not have even been aware of their handicap!
I have some of each types of shotguns, but I just have a preference for Ithaca M37s. They just carry and feel nice.