I can only speak of London - it is very rare to see oxes there. In fact, in my various visits to this city, I actually never saw an ox on the streets. In Oxford I would expect some, though. Oxford is in Oxfordshire - look how many ox-names there are. It's actually not so far away from London.
Can confirm. Used to commute daily through Oxford Circus in the centre of London for work and don’t recall seeing a single ox even there.
Therefore since we know there are oxen and they are not in London (even in Oxford circus) they must be in Oxford.