Wow Tails fans!
Here are SIX sweatshirts with JUST TAILS as the star. Tails doesn't appear alone nearly as frequently as Sonic, so any of these are really cool to see. These all arrived in the Sega Shop online at about the same time which was late summer 2018 through fall & winter.
The first 2 are just a black / white variant of each other. It has Tails in the winged ring & the "25th Anniversary" logo on the ribbon under him. The 3rd shirt is dark navy blue with a small Tails face patch in one upper corner. The "Sonic Swirl" hoodie is gray, but it has flying-forward modern Tails in that 'spin' shape, but it's yellowish.

The 5th is classic style with some neo-classic Japanese-styled art of flying Tails carrying feet-lifted Sonic in front of a triangle & stars design. The last is a zip-front coat they're calling "Bomber Jacket" which just has a white 25th logo, but Tails' name replaces the "Sonic the Hedgehog" portion on the ribbon. Note that it is more expensive at 60 to 65 dollars.