It's a hugely popular event. You, as a foreigner, can buy your way to a place via a travel package - this is not an option for British runners.
Your other alternative is a charity place - a route a lot of British runners have to take, as ballot places are limited.
So if you want to 'tick off' the marathon majors, get your credit card out and don't expect any sympathy from British runners who can't get a place.
Alternatively, if you are interested in running marathons, there are loads of others.