Can you check, if it is possible to add an user to particular usergroup on subscription activation (Membership pro)? If yes, then you can assign user that usergroupA (for example) and in JoomProfile you can go to usergroup screen. And for each user group which can search, set all usergroup except usergroupA in "Not Searchable Usergroups". In this way only "usergroupA" users will be displayed. in search result.