Where I live adoption by JW's is very rare. The blood issue is number 1 however adopting thru the ministry the concerns of being in a high control religion also come in to play.
There are times a JW can adopt - if you found a bmom who would choose them then the ministry might agree to it. I know of one such case or a step/child. Having the ministry "place" a child with "active" JW's would not happen. They wouldnt get thru the first homestudy visit. Now a "week" couple whom were very good at lying or knew what to say and didnt mind "denying" Jehovah might squeek thru.
I know this road personally - I walked it. I wanted children no I needed to be a mom! We were not able to and the only options left put our religion in question. (egg donaor and adoption)
Fast forrward many years : We are OUT and have succsefully adopted 2wice!!!!!