Va courts are governed by the county, you can try loking your local court house up online, by going to your county website, and see if they have any forms listed online for you to fill out and print at home. The adult adoption forms are usually the same as a minor form, you simply are going to check a box on the form stating that the adoptee is over the age of 18.
There is also a legal service called rapidlaw.com, which claims to have adoption forms for every state for a low price. For a slightly higher price they will fill everything out for you. I have never used this service, nor do I know of anyone who has, so I cannot tell you if they are a good service or not. I would try calling the courthouse, or looking them up online first and see if you can get the forms through them.
http://stepparent.adoptionblogs.com/