Melodic etudes - in two volumes - at the medium/medium-advanced level by the noted Russian brass composer. This is standard repertoire for the conservatory tuba player. Volume 1 of this two volume set contains the first 42 studies.
An enterprising fellow, Daniel Clouse Emerson, has written counterpoints to these Blazhevich Tuba Studies as part of his DMA studies. Here is a link to the PDF. The link goes to page 51, the beginning of the counterpoint parts, but if you scroll back to the beginning, there is a lot of information on Blazhevich and these works.
"For a younger tubist working on getting a centered tone, these studies are very useful. Consider playing any or all of the etudes at a FFF volume (or louder), with a hard marcato attack on _every_ note. Play as loud and ugly as you want. It's like being in the batting cage. The point to get centered and strong. You can back off later when it's time to make music. Study number 9 is a great example, but all of them can be played this way."
-- suggested by Jim Self