I have just spent 3 months in Ajijic and have seen the occasional SUP boarder on the lake.
I have not managed to track down anyone who is interested in paddle boarding, or who knows of a convenient place to store or launch a board here, let alone rent boards. If there is anyone who is either already SUP -ing or is interested in SUP -ing please reply to this post.
If there is any interest I would bring my board with me next year.