There were some on ebay last time I looked.
My almost 7yo and her friends are quite happy in the TP boat-shaped pool/sandpit that we've had for years (although not had sand in for ages).
Alternatively if you have a garden that's a decent size, how about an aquaslide and a hosepipe? You don't need a slide to go with the aquaslide, you can lay it flat on the lawn. As long as it's wet, it's great fun.