They were on the options list I found for 71. 73, 74 and 75 options looks like only way you got a right mirror was if you ordered dual sport mirrors. I don't have list for other years.
I have seen the standard mirrors on both sides so I don't think it was only a sport mirror option. Most who optioned the second mirror probably stepped up to the sport mirror option. Actually, my 73 swinger had the standard mirrors on both sides.
