Amazon seems like they have them all. Would it be weird if I bought all of the recordings?! I can get all of them if I buy them used. I need to remember to start going to Amazon for all of the oldish cast recordings that I want instead of iTunes eating my money.
Just want to mention the '94 JAY recording, notable for including the complete score -- all the original dance music, including Small House. While Valerie Masterson and Christopher Lee are not my favorite Anna and King, Tinuke Olafimihan is a fine Tuptim, and it's nice to have all the music. But for me it's one of those scores that requires multiple recordings.
I also agree about having multiple recordings. I think I have all the ones mentioned except the Donna Murphy revival, the Julie Andrews studio cast and the '94 Jay recording (which I was previously unaware of, but am tempted to buy because of the completeness!).