National parts depot has them in the mustang catalog for 42 dollars part number 9d612 5a right hand side and 9d612 5b for the left hand side .I would call them to check availability.
Check O'Reilly Auto parts and you can find the same size ones to take apart to replace the seal inside your originals. Search part #Niehoff FE714. They are about $15 each.
Do not overpay for replacement ones that is if you can even find any.