Well, basically:
Support: A support gun aka machinegun aka "bullethose". Check rules for specifics on weight, ammolimitations and such. Appart from the big gun, not realy anything else of importance as far as I can see.
Medic: Armband and a shitload of bandages (i.e. ripped up sheets or any other white cloth). Appart from than, any old gun you have. Oh, and check rules about armband...
Engineer: As far as I remember (again, check rules, as you will want to do anyways) you need a pair of wirecutters and a screwdriver. I guess a multitool would be enough for any needs you might have.
And about shops. Check
http://www.airsoftsverige.com/ under the "Återförsäljare"-board. They have a good and long list of places both swedish and not (might have to check them, all as there's no sorting on country, but still...). What is good is up to you to decide, if unsure, search the board...