Get them from Jon B. They are $1050 from the dealer for the set.

I had the opposite issue, needed the track extension. I bought a sheet of 1/2 plastic for $200 from the local mom/pop hardware store. It was advertised as dairy grade, useable for cutting boards. Lowes/home depot did have the metric T-nuts to press into the holes, had to use a similar sized SAE thread and new bolts but it works. The only thing I didn’t like was that it came in a soft white color, but I painted it.

Also, sheet was large enough for me to make 5 track extensions.

I made it in a hurry prepping for a track day, looking for pics. I used the street extension as template onto cardboard and penciled in the extension piece. Marked the mounting holes on the template. Cut it out with an exacto knife. Transferred the shape to the plastic, drilled my holes, tapped the T-Nuts in and was good to go. I’m in Afghanistan right now, don’t have everything setup to upload photos. I have cell phone shots, don’t have my phone on me, will try to follow up later with better shots if I can find them.

Well, I can’t even copy and paste on this anti-hack computer so I’ll be back.