CATERHAM will pick up some 20w-20, if they run out of 10w-30.
Interestingly enough, I came across some actual 10w the other day, too. I committed the cardinal BITOG sin and didn't look over it carefully (or even note the brand!) to see how dated or recent it might be. This place had everything from Castrol 0w-40 (very recent in Canada) on the shelves to the clear bottles of SM/GF-4 Quaker State synthetic. So, it could be anything.