I think most manufacturers still offer copper coils in at least packaged units, most switched to aluminum about 10 years ago because of massive amounts of lawsuits due to leaking copper coils, which all goes back to govt mandated efficiency standards. Since the switch to aluminum we saw a HUGE decline in coils leaking under warranty, when I worked residential. Theres also some aftermarket coil manufacturers like ADP that still make copper A-coils and are generally less expensive than the OEM coil

 

Most are now all aluminum but you can find some copper. Personally I wouldn't want a copper coil, man have we changed a lot of them. Obviously you can get leakers in aluminum tubing too.

 

ADP and Aspen, Mortex probably still make some.

Make sure to register the coil of choose as you may get 10 years whereas not being registered it may default to a base warranty of 5 years.

If your going with a piston metering device, those typically need to match your OD unit. You could check the existing piston size and match to the new coil.

If coil was registered initially and your the original owner you probably have a 10 year coil warranty, labor and associated parts are chargeable.