Concertina blind for Lunar Delta.

Seitz is the correct name.  Leisure Shop Direct seem to have what you want.  However, the dealer from whom you purchased the caravan cannot just wash his hands of the problem.  Assuming the caravan is still under warranty and that blinds are not excluded (see your warranty documentation) you have strong rights in law.  Your purchase contract was with him, not Lunar; so he is responsible for a guarantee claim and as the item is easily available he has no excuses..  A gentle reminder to him of this, citing the Sale of Goods Act,  may do the trick; if he refuses speak to Citizens Advice  who will provide you with draft letters to send. Be polite but firm.

Many thanks comeyras.  We had wondered about this ourselves, and we will certainly check out our documentation.  The dealer just said they can no longer get parts for Lunar but as this isn’t a specific ‘Lunar part’, many different caravans seem to have these blinds, we did feel a bit fobbed off.