In about 20 hours I will be leaving for a trip that will take me to London. My plan for getting around while there had been to get an Oyster card, but at the last moment I discover that they have to be bought in advance. https://www.tfl.gov.uk/travel-information/visiting-london/visitor-oyster-card says:
It is not possible to buy a Visitor Oyster card when you are in London.
Apparently as a non-resident I was supposed to have planned ahead and bought the ticket by mail order before leaving home.
Do I have any option left for avoiding paying single-ticket fares for everything? Are one-day travelcards are still available without having Oyster?