If you really want to meet Sumo wrestlers, you will see it here in Ryogoku. There are some Sumo Gym which has open window for practice room. So, you can also watch Sumo Practice.
Try Chanko-nabe which is what Sumo wrestlers are made of. Chanko is one of Nabemono (鍋物, なべ物, nabe cooking pot + mono things, stuffs, kinds) which (鍋物, なべ物, nabe cooking pot + mono things, stuffs, kinds) or simply called Nabe, is a term referring to all varieties of Japanese steamboat dishes, also known as one pot dishes. You can find the best Chanko restaurants which run by Sumo wrestlers.