Barbās explanation is right, but in real life people donāt follow it 100 percent. You can actually say that you bought a ticket to London or a ticket for London, but ātoā is better.
There are some expressions in which both ātoā and āforā are correct in regard to destination:
āWeāre headed to London.ā
āWeāre headed for London.ā
Those two sentences mean exactly the same thing.
So the distinction isnāt rigid, but if you follow Barbās rule you can at least be sure youāll never be wrong.
Isnāt āa ticket for Londonā a short form for āa ticket for the trip/train to Londonā and āa ticket to Londonā a short form for āa ticket from here to Londonā? If so, each form would have a different underlying thought behind it, though the action would be the same in each case, i.e. ātravel to Londonā
Itās possible that shortening or ellipsis are occuring:
How much is a train ticket for <the journey/trip/train to> Waterloo station?
1a. How much is a train ticket for <arrival at/getting to/travel to> Waterloo station?
How much is a train ticket to Waterloo station?
Is this the express train for <the journey/trip/train to> London?
3a. Is this the express train for <arrival at/getting to/travel to> London?