Here in the US they sell 4 foot fluorescent light tubes all the time. Why not look at a home improvement store, rather than a fish store? If there is already a glass lid, you could just suspend the lights over the top fairly easily and then you wouldn't have to worry about the length.
8 feet long tank!!!

I can only imagine what that must be like!
If I can give you a piece of advice, before filling it up for the first time, I would bring an inspector into your home and check out the structure underneath where you are going to be placing this leviathan tank. 1100 liters is quite a lot of weight. (That's well over a ton in water ALONE!) Fortunately, it will be spread out over 8 feet of length, but I think it is better safe than sorry.