I believe this strap material was the same used for the rear license plate shield just below the rear bumper. An original can be cut into strips to make an OE strap
I would respectfully disagree at least if your comparing the upper PS hose straps discussed in this thread.
The originals of both items you mention and I have here are pretty different in make up, thickness and final look. The light shield is a single layer with random reinforcement threads while the PS straps have multiple layers and are three to four times thinker as well as having a nylon reinforcement cloth sheets in one or more layers. Similar to plys in a nylon ply tires used during the 50s and 60's . Much like what we find for holding up the heater hoses in the engine compartment on some 65-66 applications
Some examples suggest that the PS straps were made from recycled tire side walls. some with even the white wall visible or with a white exterior layer like we find on muffler and exhaust hangers. Some have ribs in the last outer layer that are orientated on an angle to how they were cut
Picture showing the relative thickness, layers or lack of multiple layers and other close up details.
You can also compare the pictures earlier in the thread with the uniform nylon visible
Some more 68 upper examples
http://www.concoursmustang.com/forum/index.php?topic=11041.msg39709#msg39709