Muscle Car Research (my company) is now selling reproduction 1969 and 1970 Mustang and Cougar cowl vent seals. Cost for a pair of seals is $25 plus shipping. I reverse-engineered this part using an original seal and vent as a template. Picture and purchase details can be found on my company web site:
http://www.musclecarresearch.com/vent-sealsPayment can be made using PayPal (credit cards can be processed by PayPal, too), check, or money order.