Good question. I just googled "moms of boys" b/c I've been longing for a forum too and found this: http://www.momsofboys.org/ Didn't read much but it doesn't look religious at first glance.
I agree that it helps to let yourself feel sad. There is a loss involved. When I was pregnant with DS1 and had GD, it changed once he was born. GD did not go away completely but it changed signficantly and I cared a lot less. Now with DS2, I still get moments when I realize what I may miss out on by not having a daughter and I let myself feel sad. Then I look at him and remind myself I'm also lucky.