snap

Buy from Antnet Digital in Brunete, Madrid. They are Invacom's main agent in Spain and will send one, and should be able to supply the adjustable feedhorn you will need. They usually have a large stock of LNB's.
Sorry to hear the dish is a Fortecstar. I have one of these gathering dust in the basement. (it was so bad I couldn't bring myself to even give it away)
Not only are they an absolute pig to set up, when you do get it done the gain is nothing like as good as a good quality 2.4 metre, more like a good 1.2 or 1.5metre offset. The only good thing about them is that they are cheap, but that's for a reason.
Sorry to be so negative, but in a place such as costa Blanca, where the signal is so weak, there's very little alternative to spending money if receiving the BBC is the objective.