I found some time to play with good old Terragen and made 4 free skycubes for you. There is also a correctly uv-mapped cube model within the package...in case you want to exchange the one from sphere-engine (wich isen't well mapped)...or if you need fog displayed on the sky (wich doesen't work with A6 skys)!

You will find them on my website under Models->Freebies

4 SKY-CUBES