The importers have none is stock until at least Novemeber so you would have to find a retailler with some on the shelf.
I have a couple of Synmats (my preference) in stock. Let me know if you are interested.
There's no hurry, we won't use them until next spring.
The Synmat that I tried (in the shop) yesterday seemed less bulky than the (sample) Downmat, and felt just like an air bed. We haven't had good experience with air beds in the past which is why we've been sleeping comfortably on the Thermarest-like Fat Airics which are 7.5cm thick.
Why do you prefer the Synmat?
EDIT: We got two Exped Downmat 7 DLXs today from The Outdoor Shop in Stony Stratford!