First of all, hello! I'll also be starting my PGCE at Oxford in September, but I'll be doing RE. I also had to track down foreign CRB equivalent checks, but unfortunately I can't help you with Spain specifically. What I can suggest from experience, however, is that you call directly the agency providing the background check (in this case the Ministerio de Justicia). I know I became all flustered trying to follow all the instructions given on the consulate websites of the two countries, but when I called them with my questions it turned out that I was getting all panicked over nothing. One consulate told me things like, "No, contrary to what the website says, you do not need an apostille." And the Israelis yelled at me in Hebrew for being an idiot and making things more complicated than they had to be. It was a little awful, but it ended up making my life a lot easier than I had been making it. Anyway, sorry if that's useless advice or you've already tried it without success. Good luck with dealing with them, and I guess I'll probably see you around in September!