Using any button front shirt pattern that includes instructions for a band collar in addition to a conventional shirt collar these instructions on this web site will guide you to making a clergy shirt.
The pattern companies will sometimes have them is stock if you call them. Especially if the pattern is not listed on their site. I have gotten quite a few older patterns that way. --Judi
Here's the link for Simplicity They offer "out of print" patterns on their web site, too.
http://www.simplicity.com/c-164-c...
You might also want to try the following http://butterick.mccall.com/relig...
I hope this helps.n *'s
Have you tryed googling it? You can also try etsy.com or ebay. Pattern Review often has out of print patterns, too.