Hi Travis,
Here’s a site that has a bunch of min’yō lyrics from different prefectures to get you started:
http://www.benben.jp/minyo/index.htm
There are lots of books available in Japanese with lyrics for the top 200 or so min’yō, and they are pretty cheap compared to every other aspect of learning shamisen.
Singing min’yō by itself can be challenging, and singing while playing is quite a bit harder. Singing Tsugaru songs while simultaneously playing is maybe the hardest thing to attempt – I think Takahashi Chukuzan II is the only person I’ve seen do this in performance. So my advice would be to work up to that. Start with singing easy min’yō (like tanko bushi, or hanagasa ondo, or dompan bushi) and work up to singing and playing together. And listen as much as you can – the basic melody is the bare skeleton, but timbre and embellishments are what make min’yō interesting to listen to, so be mindful of those things. There are a lot of performances on youtube, and watching them is a great way to see how the music is embodied (watch the singer’s mouth, how he moves his head, his posture, etc – all of this goes into making the ‘best’ sound).
One other thing is that min’yō don’t have a fixed set of lyrics. Usually everyone sings the first verse of a given song with the same lyrics, but after that, there might be 30 or more verses to choose from. I studied this pretty thoroughly in the 90s, using about 10 different songbooks and compiling the lyrics for each song from each book. I was surprised how little overlap there was. So what I’m getting at is that after that first verse, you might not have the lyrics that you are hearing on the recording. After some practice, though, you should be able to read a lyric and basically guess how it will be sung.
If you are looking specifically for Tsugaru songs, send me a message and I’ll send you some scans.