Hey all thought i would share my answer to an insert. Its not exactly what i wanted but it works and should fit the board extension and invaders from afar. FYI i use black bristle board for the bottom to save space. Token and Card tray 28.8cm x 11.9cm x 4.2cm tall
Your local arts & crafts supply store should carry it.
That's where I got mine. I bought a big sheet of foam core and bristle board for like $10 and it's been enough for these trays, my Imperial Assault trays, and plenty left over for more games. Highly recommended.