Remember being told these covers are v. expensive to buy new.
I bought a used spare+cover a couple months ago. I'd been chancing it with no spare and a can of 'inflate 'n seal' / 'hope n' pray' (for 1 year and 6000 mi of weekends away). Suspect there are a lot of GTAs without spares out there.
How's your French ?
http://www2.alpine-renault.net/annonce_ ... php?id=187[url]
ad dates from December but it might be still available - think "avec sa housse" means "with cover". If the cover is good 60 Euros could be a fair price for the cover alone. (but I'd check what the price new is first).
Could be worth a go if you can't get a cheap/used cover from the uk.