The difficulty is that nobody can be certain that wherever you go geographically within reach of seeing these, a) they are going to be on display or, b) that the weather will co-operate (i.e, no cloud to speak of). You could try going to Iceland, and stay up well into the night if the weather is right. Equally, Norway, Sweden or Finland are candidates and they have been known to be visible in Scotland. There is absolutely no need to involve any tour operator - all you need to do is check out the cloud cover on the day (well, after dark) and if it is almost completely clear then head out of town away from the street lights - this is perhaps the most difficult part - then look up. Ask locally as to in which direction the phenomenon is most commonly seen. They are far from appearing as predictably as the sun, moon and stars - some nights they do, often they don't.