I would very, very highly recommend Larry Miller's "You can play the Cajun accordion". Comes with a CD with many old time tunes mostly by Allie Young (worth the price all by itself). He starts out with the basics, fingering singles, octaves, bass notes, tablatures for various tunes. Demo songs on CD follow instruction. A great start. My first song was "Colinda".
Beau Jocque's first release, "My Name Is Beau Jocque" was what I learned on. Very simple tunes. Guess you need a Bb accordion, though...
Other than that, it may sound silly, but "Toot Toot" is a great first song to learn. I'll bet the melody is already "something you can hum", and that is the key to learning *any* song, brutha! -- Cajun, zydeco, rock & roll...