There are all kinds of perlon needle felt out there. (Very similar to bass box covering material out there).
There are various shades of gray and black and in between.
The correct color is charcoal and matches almost exactly to the headliner material on the inside of the targa top.
The closest match I could find was from
http://www.appbiz.comThey sell the perlin charcoal felt by the yard.
Also try Heidi and James (in our vendors section that make all the fiberglass interior parts and carpet kids). They have some perlon felt that is close too!