Those userrs are stored in groups with special names, here are the names assuming the category id is 1.
cid:1:privileges:find
cid:1:privileges:read
cid:1:privileges:topics:create
cid:1:privileges:topics:reply
You can get the user ids from these groups by.
Groups.getMembers('cid:1:privileges:find', 0, -1, callback); This will give you all the user ids that have the find permission for category 1.
If you want to get their basic info like username picture slug so you can show user icons you can just use Groups.getMemberUsers('cid:1:privileges:find', 0, -1, calllback);
