We have a wide variety of tuba mouthpieces, available new or second hand from manufacturers such as Arnolds, Denis Wick, Vincent Bach, Parker and Yamaha. They come in different sizes and dimensions to better suit the player. A choice in mouthpieces for a player is entirely subjective, and what would work for one player may be entirely different for another.  A popular size of Tuba Mouthpiece is the 24AW designed originally by Vincent Bach. This model has been copied by various makers, some not very accurate. The German made Arnolds 24AW is a very good high quality copy & sells at less than half of the price of the original.