Neither of us belong to a particular church group or religious organization. How do we go about finding the officiant right for us?
A civil servant's primary role is to legalize the marriage, so unless you're marrying in Massachusetts or California, that won't be a part of the ceremony. Instead, you can ask a judge or justice of the peace to sanction your union symbolically. Also, look into an Ethical Humanist officiant (to find a local society, visit American Ethical Union or an officiant from the Unitarian Universalist Association, Universal Life Church, or Metropolitan Community Church. These groups have announced their support for gay marriages and encourage their clergy to officiate them. And keep in mind that your officiant doesn't have to be "official" -- that is licensed to perform legal weddings -- which means a dear friend or relative can do the honor.
If you'd like a religious ceremony, look for an officiant from a religion that leaves the decision up to individual clergy members (Buddhist, some Protestant, some Quaker, and Reform Jewish). Many religious denominations also bless gay unions, even if they won't officiate these unions. Of course, the Internet is a great research tool for finding local officiants, and many invite gay couples to contact them about creating a personalized ceremony.
Knot Note: If you choose a religious officiant or another person affiliated with a group (such as an Ethical Humanist), he may give you sample ceremony wording to work from as a starting point. The more secular the officiant, the more creative license you will likely have over what is said, read, sung, or played during the ceremony