Why can't I get those CDs?

So I read the Fonoforum and the Strad, both of which have recommended CDs. Found a few that are interesting, but really, what is happening to amazon? There are three which I really cannot find, including:

• Charles MacKerras recording of Mozart Symphonies 38-41 with the Scottish Chamber Orchestra (I know I have the pieces already, but not this recording)
• Vivaldi's Concerti per violino II 'Di sfida' with Anton Steck (they might be some I don't know, especially since four of them had not so far been edited)
• Vidor Nagy's recording of Viola trios, by Just, Holzer, Glinka, Berger (whoever some of these are, but I like obscure viola repertoire).

All these have had good reviews, but I can't find them. Bit of a pain, really. Previous experience has shown how fast specialist CDs disappear from the shops, and before you know it, someone expects you to pay 150 Euros for them. Over this Scottish dead body!