Hello Patty Osowski,
Here is a link for aqua training:
Natalie aka NAPS 2 B Fit.
I would suggest that you get yourself a general aquatic exercise certification even if you want to make exercise for arthritis your focus. While many organization dabble in aquatic exercise, I have found the Aquatic Exercise Association a trusted place to go to http://www.aeawave.com/Home.aspx.