Word has cone down from the Home Office that the wheel requirements stated in the Race rules are to stand. The
16×11.7 wheels are still available from Pendle

policar-aluminium-f1-rear-wheels-16×11-7.html

Also at 132 slotcar.us
pw16011724a-aluminum-rear-wheels-2-early-70s-f1-cars

-Marc (Datto)