Seems like Miguel is out of business in Mexico for these. I believe Layson's is now importing the Mexican lenses directly since their Australian connection has been broken since Covid. Also Classic is now stocking Layson's parts for the 66 now too,
https://www.classicindustries.com/shop/1966/plymouth/valiant/parts/?q=tail light
But there is a new kid on the block... anyone use these yet?
1966 Plymouth Barracuda Valiant Tail Light Lens Set LH/RH — Schimmel Engineering