No problem on the source. It was a "dress shop"/ cloth store.
The red material is something more or less used for sports jerseys and the like. Very transparent on the acoustic end. The charcoal black gray silvery stuff is liner material used as in between material on heavy fabrics. coats draperies etc.
When I went to the store with a sample of my old speaker cloth. The seamstresses that run the place knew exactly what I had and what I needed.
Got the red stuff for $1.92 a yard so I bought 2 yards. Enough to do two sets of redlines. The black liner material was a little more expensive. I thinks about 3 or 4 dollars a yard. It works, it is is transparent, stretches easily and in the case of the red material they offer other colors as well.
You could also try JoAnns if you have then down in the Carolina's.
Here are a few pics of the crosses out of my 60's and 60.2 which neither are the same as each other nor even like the one in Mika's photo. On the 60's I also had to install two Peerless passive radiators to replace the missing ABR's. That worked out well to.
Sorry for hogging up the page.