Hi,
i dont know why you need the admin user_ids but you should get the list of public folders with this query:
select
cri.item_id,
cri.name
from
cr_items cri, fs_root_folders frf, site_nodes s2,
site_nodes s1, dotlrn_communities_core dcc
where
cri.parent_id = frf.folder_id
and frf.package_id = s2.object_id
and dcc.package_id = s1.object_id
and s1.node_id = s2.parent_id
and s2.name = 'file-storage'
and cri.name = 'public';
you could use a pgsql to go thru all of the folder and change permissions.