You can use the following report to get all local administrators.
Select Top 1000000 tblAssets.AssetID,
tblAssets.AssetName,
tblUsersInGroup.Username,
tblUsersInGroup.Domainname,
tblUsersInGroup.Groupname
From tblAssets
Inner Join tblUsersInGroup On tblAssets.AssetID = tblUsersInGroup.AssetID
Where tblUsersInGroup.Groupname = 'administrators'
Order By tblAssets.AssetName