I'm a 16 guage fan, so I'm a little biased

I have no problems finding loads for turkey for my 16 guage. Remington Express in #4-#6 is plenty capable of killing a turkey. Also Kent makes some excellent 16 guage loads, http://www.kentgamebore.com The shells don't say "Turkey Load" on them but they are getting 13000fps which is as fast as a 12 guage 3" Winchester High Velocity load.

I get my Remington Express at Dick's here. I don't know about your selection in your area though. If you can't find 16 guage locally then the 20 guage might be a better option.