Don't know what one you're needing, but a few years ago I got a replacement fan clutch for the 440 in my '70 GTX from Advance Auto that was unbelievably correct, even had the same part # on it. If I remember right, the only difference from the original that I could find was slotted holes for the fan bolts instead of round.

The brand name was Imperial, pn 211049. Whether or not it's still available I have no idea, but hope this helps.