How can I attach to drywall with aluminum studs?
In North America, studs are usually installed 16" on centre, regardless of whether wood or metal studs are used.  (Commercial interior walls may have different spacing.)  If you can't find the stud with your stud finder, look for a plug or switch on the wall - they will be attached to one side of the stud and then start from there.

Just use normal fine-thread drywall screws.  Drywall screws are available in coarse thread for wood studs, and fine thread for metal studs.

PS: Are you sure the studs are aluminum?  All metals studs that I have seen are galvanized steel.