They imported the 10 gauge TM one time when it first came out. I had a partial box somebody gave me a couple years later. But when I called and asked about ordering more the people at Kent USA acted like they didn't even know what I was talking about. The guy on the phone nearly called me a liar when I said I'd actually owned some of the shells. Wish I hadn't shot them all up, I'd have sent them a photo.
I've actually seen a few of the Gamebore 8 gauge shells here in the US over the years. I've got a 10 pack of them in black powder that Kaas gave me awhile back. I think New England Arms used to import them somehow but they've been out of business several years unfortunately.
A gentleman did a posting on here last year that he'd spotted some Bismuth Cartridge Co. short 10 gauge at a store in Virginia. I happened to see the posting early in the AM and called as soon as the store opened. Got lucky and they still had them, I was the first one to call. Bought all five boxes and I haven't been able to make myself shoot them because they've gotten so rare. Figured I'd save them for a special occasion, they're all large size shot so I'll use them on geese sometime.
DLH