These mirrors are readily available from Mustang sources, in either NOS or reproduction formats. Mustangs Unlimited (1-800-243-7278, or
www.MustangsUnlimited.com) lists them:
'67-68 standard rectangular, LH or RH (same mirror used on both sides)
Original: F2406, $53.30
Repro: 67696A, $39.95
As info, these mirrors were not factory items..instead they were LM dealer installed. Many owners have toss them by now for modern replacements.