Regarding 6 months without sun in the Northern European countries - I see your point, Scotland is not the sunniest place on the planet, btw
Solutions are:
1) go for a vacation somewhere sunny
2) go to the mountains (nearly all Norther European countries have mountains) to be above the clouds and get some sun. Skiing is great for so many reasons (provided you can do it and will not end with your legs broken in a hospital)!
Ionic showers and UVB lamps were invented for people, who have shifts in Arctic/Antarctic stations, where its -40/70 degrees Celcius outside and you really have 6-months-long nights. All the rest of the world receives some sunlight now and then. It's actually up to you (as always, in fact) how to treat your body, how to get calories and vitamins and how to excercise (or not). Therefore, people with determination will find a way to get some sunlight even during long cloudy winters. On the opposite, lazy people prefer having a pill and sitting under the lamp.
Even if there is not much sun outside, yet you still can go outside for a walk (and not freeze to the death) - do it. Going outside is always 200% more useful for your health than sitting inside your house. And if it's pouring rain for a month or snow falls for a week and it's 6-meters-thick already - I'd say you have biggger concerns than vitamin D deficiency