Custom made doors.

Cutting down 80" tall or even 78" tall doors will destroy the structure and the look---unless they are slab (flat) doors.

I've shortened hollow core slab doors and reinforced the bottom by replacing the structural elements. I was pretty cheap labor and still charged $20 a door to do that.

If you can find a style with slid wood at the top and bottom of each door you might be able to cut them down.

Some styles have a decent amount of wood at the top and bottom.

Lumberyards are real Millwork Suppliers should either have or have available 6' tall bifolds or blank doors to make a 6' tall bifold unit.

Try a habitat for humanity restore. In my area they often have many styles of solid wood doors that depending on the style could be cut to size.

i make doors and i have never seen stock doors 72". thats a custom size. you can have them made or find something with the integrity too cut down.