I used a local Sussex supplier who sourced his doors from Warm Protection which is based in the North East. I had very good service from them the door does go up to about 12" x 12" when rolled.
Worth contacting direct and asking for a local supplier.
As I understand it I believe they buy in the slats ready made from Germany.
I suspect many of the "manufacturers" of roller doors in fact buy in the slats from one or two specialist companies as they all look suspiciously similar.
Word of warning I had a few slats that buckled, a search on the net confirms it is a problem that pops up from time to time due to incorrect filling of the slats with insulation causing uneven expansion in sunlight with different suppliers.
A suggestion is that at the start of a production run the foam is not flowing correctly. One guy was having to sue his garage door company (one of the national brands) because they refused to help.
I had excellent service both from Warm Protection and my installer they changed the whole curtain quickly, although only a few were affected and without a quibble to ensure the problem was resolved.
The new one seems fine, that's what counts for me not a cheap price or gimmicks but good old fashioned customer service.
Wouldn't hesitate to recommend them.