find a sheet metal shop in your area, most hvac companies have a shop in the back
buy a 8' long strip of duct hanger strap 1'' wide
go to a welding shop, you want a piece of 1/4'' flat bar 4'' long
you also want a 1/4'' flat bar 2'' wide x 4'' long
either. drilll bolt the 1'' onto the 2''
or. weld the 1'' to the 2'' make a jig
cut a strip of the strap 3'' long, set it on your jig
beat it with a hammer.
now you have a clip