A few questions:
How good are you and your friend? I can go all out if you want. Maybe specify how high you can play so I don't make it too hard because Alto is a fun instrument to write for.
Are you sure you can only do a duet? Maybe there is somebody else that would play a Tenor or Bari part? It would sound more fullfilling but I can do it. It's just the chords will suffer. So let me know if that's a possibility or if it has to be two altos. again thats fine.Let me know.