Well, what sort of thing do you fancy? If you don't run well in warm weather that's important to know. If you're strapped for cash and need somewhere you can hitchhike or cycle to / camp at then that's important too. If you're definitely superkeen on a city race or a certain level of support, or conversely could be swayed by somewhere e.g. very scenic but quiet...
In the UK... big cities... Manchester marathon is starting up again next spring. And Edinburgh is probably not full yet but it is plagued by problems of one sort or another... it just seems slightly unlucky!
There are loads of little UK ones. Usually vaguely scenic, pretty much always friendly, but not really hordes of screaming supporters.
If you're up for a cheap flight + hostel (or more) there are nice city races all over Europe. I've done Hamburg and Zurich (to name 2 spring ones) . Take a look at the reviews on marathonguide.com and see what catches your fancy. People like Barcelona & Seville too so I hear. Then there is Rotterdam for fast times (heatwaves aside) or Paris for having people pee on your feet (allegedly ;D). Lots.
Or if you fancy a downhill one (net) and aren't worried by having NO SUPPORTERS OUT THERE AT ALL then Malta is at the end of Feb and has a medal like a brick.
I suspect that not getting in may be the best thing that ever happened to you 