Question from a friend, but I'm curious too.

Is it possible to buy a single London Underground ticket (e.g. zone 1
only) from an NR ticket office many miles away from London (in this case
Yorkshire)?

Ditto for buying an inboundary Day Travelcard (i.e. zones 1-6)?

FWIW, in this case, using contactless cards aren't an option, nor is
Oyster (several are travelling, but either not enough for the 10+ Tube
Group ticket, or else they wouldn't be able to travel all together - I'm
a bit murky on the details of this endeavour).

I know it's possible to get online booking engines to offer inboundary
Day Travelcards, but they can't be made to offer single Tube tickets.

Can an NR ticket office sell them? I've had a quick fiddle with
BRfares.com ("zone u1* Londn" etc) without much luck.