You don't need to import from the US. There are some very good manufacturers in Europe, and one alleges to make roofs that are shipped to the US for distribution.
I got my roof from Cabrio in Germany. I have found them to be excellent. Their website is pretty good also, and is in English and German. (
www.cabrio.de) They cut their own tops and have a mass of colours. Their service is excellent in my experience. A number of forum members have used them also.
I believe all the tops are the same for all cars regardless of engine size or slightly different frame design. You will need to order new wires, and will also need to order the two foam things that go atop the door windows to ensure a good fit. I think that's about it. They have all that kit.
I did my own top; it's quote doable with help. I'm in SW London if you're close by. PM me if you want to take a look and talk it through.