Any forum with a marketplace where you are allowed to post a request to buy forums, or where users can offer them, would be the right place. http://wetalknation.net/marketplace is such a place.
I am equally interested in acquiring sites who need a restart, or are about to die theirs, but would rather see it live on on the net in some form. Or those who finished building theirs and want to sell it of to a new owner. I just hate seeing sites die when it wasn't needed.
Turnkey is when something is made to be sold to another owner, for example, a manufacturing process sold by an industrial engineering company (plastics molding plant), when the plant is up and running they give the key to the owner, he then starts making plastic parts, thus he purchased a turnkey plant from the industrial manufacturing engineering company, now he has to run it with his own staff.
We are thinking on two different levels of active ...... I'm thinking of a start up forum.. Maybe 10k+ Posts 20-30 Active Members lol .. My definition of active is a little different then some peoples, sorry.