UK is part of EEA, so no importing is done at all, no customs, you can get the price without VAT if you have the VAT identificator etc. The only difference between buying something from let's say Germany and UK for any member of EEA is the currency exchange ratio, everything else is the same. Unfortunately usually these parts are not sold separately in Europe, the European Lian Li distributors simply don't import them. Your best bet is to get one from a used or new case unfortunately.
That is incorrect, both Finland and UK are members of European single market and your customs CANNOT put Finish VAT on top of the UK price which already includes the VAT. Ordering from UK is exactly the same as ordering from Germany. The only thing i can think of is that you bought something from eBay UK, which in reality was shipped from Asia (Hong Kong, Taiwan). In that case, they were collecting imports taxes and VAT correctly. In case of UK, there are none, seriously. If it is shipped from EU member state to EU member state, there are no customs and technically it is the shop which should set the correct VAT according to the destination country (Amazon UK does this, many other shops don't). The other possibility was if it was shipped from Channel Islands, but you could just ask kustompcs to be sure. http://www.finlandforum.org/viewtopic.php?f=3&t=54641 PS: Shipping would be pretty much the same from everywhere, so you can't save much on that.
Did you provide them with your VAT number ? Otherwise it makes no sense whatsoever, and i would try to ask customs in Finland why, because that is not how the European market works.