Definitely play 999 first because it is amazing but VLR is better and will ruin it. The story also 'kinda' continues from it so it would be better to play them in succession.

999 wasn't released in Australia either so I had to import a US copy. It's not too difficult to get a hold of, though. Apparently VLR got an Australian release but I never saw it in a store, but I pre-ordered it overseas so it didn't really matter.

I've had perfect experiences with these sellers so you should be fine to order from either of them (I think they both ship to UK):
Ozgameshop
Play-Asia

You might have success with Amazon UK as well but I haven't had enough experience with them to say whether they're good or not.