Do you want to fly throught them?

Or are they just for backgrounds etc?

If they are just for backgrounds, there is a great tutorial on the A|W site regarding the use of the ENV Sky node here:
https://www.aliaswavefront.com/en/Tmp...dering_m.html#

Also, downloadable A|W sky images can be found here:
https://www.aliaswavefront.com/en/Tmp...ronment_m.html

Otherwise, 2d photographs of a large sky(s) are freely available at many texture resource sites.

Do a search on this site for sky textures, or just textures in general, and you can go from there

If you want to fly through them, that's a WHOLE other ball of wax

Lemme know...