Welcome to the board. In order to differentiate yourselves from the million and one other couples looking for the exact same thing, perhaps you could expand a little on the specifics. You don't have to, of course, but then you shouldn't be surprised at the utter lack of response you get.
Do you have an age range in mind? Do you have children? Would it be ok if she has children? Would it be ok if she's married or in another relationship? Do you like going out to clubs or do you prefer dinner and a movie? Are you looking for someone for you, someone for your husband, or someone to "share"? If the latter, what happens if one of you falls for her and the other doesn't? What happens if she falls for one of you but not the other?