An inexpensive way to get some 70'S big collar shirts??? ...

Have you tried looking in charity shops as they often have lots of old 60s and 70s clothes and are not expensive.

good luck in the contest!

I agaree with Lou Lou.  Also, without doing any research, try Salvation Army or Good Will.  You don't say old you are, but you might want to ask friends to either look in their attics or have their parents look in their attics.  People sometimes put clothes up in the attic and forget about them.  If you need any thing  further, let me know.  Good luck with your contest.

Merry Meet and Merry Bide

Cheryl