Most domestic older children available for adoption come from the foster care system and your state's Child Protective Services. Be careful about paying an agency to do this, as almost all foster care adoptions are free through the state. There are agencies that will conduct a nationwide foster child search and facilitate adoption, one of these is adoptamerica, a reputable organization I know about.

Be prepared that most older children have suffered neglect or abuse, and have a unique set of emotional problems. Next, everyone's focus is on finding them a home, and complete candid information on the children is not always available. Sometimes the agencies don't know, sometimes they suppress negative info, and sometimes the children themselves withhold the core issue they're dealing with. Familiarize yourself with terms like reactive attachment and oppositional defiance. My wife and I have adopted three children from foster care, but the oldest was 16 months when he came to our home. You can do it, and it's immencely rewarding, but it takes two committed parents. Think twice if your husband isn't supportive. Best Wishes.