Rockywoods Fabrics sells the closest fabric color match for the Maine built TDBs in Mil.-Spec. 1000D urethane coated Cordura in Coyote Brown, which is a darker, more brown replacement to the original material. They also sell the Mil. Spec. 2" wide webbing and color matched side-release end buckles. These are both solution dyed nylon fabrics.
The original buckle female ends will mate with the replacement male ends, but not the converse. You would do better replacing the entire buckle.
I opted to purchase the 1000D Cordura coated and treated fabric in Tan-499, which is a near-perfect color match with the original blind panel material.
I borrowed a long-in-the-tooth, long arm commercial machine from a friend who owns a specialty XC ski outer wear company. Karen is coaching me through fabrication of a second front blind panel. I have a half-yard scrap piece of the heavy weave nylon, rubber impregnated, fabric that the Clark's original blind fabrication jobber used to reinforce the panel corners with. I think this was sent to me, along with a pint of gel-coat in response to my request back when I first purchased my TDB-14'. I have no idea whether this is still available commercially, or whether it is still incorporated into the production process in the current blinds.
Here is a link to the replacement buckle:
http://www.rockywoods.com/Hardware-Zippers/Buckle-Hardware/Nexus-2-Side-Release-Buckles-Tan499
I also purchased two yards of Mil.-Spec. 2"wide hook and loop sew-on material to close up some gaps on the front blind panel junction with the side panels.