There are many sky and sunset photos at dreamstime.com. This is an inexpensive stock photo resource with thousands of useful photos. Most cost $1 each to download.

I just downloaded a sunset to use as a backdrop in a Vue 5i scene.

In fact, digital artists might be able to sell there.

_ jc...'Art Head Start' e-book
'Art Head Start.com site Digital Art skills. Free lighting chapter, tutes, Vue models, texture pix.