Gonzaga Duets (free download)

Francisca "Chinquinha" Gonzaga (1847-1935) was a Brazilian composer, conductor, pianist, and educator. Gonzaga is associated with works in the "choro" style, which blends elements of polka and ragtime with a Brazilian twist. Not only was Gonzaga a prolific composer with over two thousand compositions, she was an activist who used revenue from her composition sales to support the abolitionist movement in Brazil. 

As far as I can tell, she never wrote anything for tubas specifically, so I took matters into my own hands and arranged a couple of her works for tuba duet. 

Água do Vintém
Difficulty: Advanced (Undergraduate/Graduate)
Instrumentation: 2 Tu (or 1 Eu / 1 Tu)
Score and Parts (PDF)
MIDI audio (MP3)

Gaúcho
Difficulty: Advanced (Undergraduate/Graduate)
Instrumentation: 2 Tu (or 1 Eu / 1 Tu)
Score and Parts (PDF)
MIDI audio (MP3)

Sospiro y Atraente
This is a combination of two different works that I found to be complimentary. You can perform this arrangement attacca or you can isolate the individual tunes. 
Difficulty: Advanced (Undergraduate/Graduate)
Instrumentation: 2 Tu (This one doesn't sit as well for a euph to play the top part, but you can make it work if you really want to)
Score and Parts (PDF)
MIDI audio (MP3)