In a bit less than two months there will be a nice selection of new Digimon t-shirts in Japan.
Six will be based on Digimon Adventure (with 3 different designs in two colors each.)
The seventh will be a Xros Wars design (which seems to have a smidge of Engrish on it...)
Source link goes to a listing of all the shirts in various sizes on CDJapan. The product listings themselves show the designs on the shirt, but I went with the image only version to show the text detail on a few of them.
Check the size detail information, as the size listing may not be the same as it is in your part of the world.