Anything particular you have in mind? What environments are you thinking of? (Brinstar, Tallon IV, etc.) Are you looking for absolutely everything, from phazon plants to Space Pirate space-station graphics, or more specific scenery?
To be honest the default scenery already covers a lot of this stuff, except maybe backgrounds for urban structure. You can make alien growth out of Soldat's regular vegetation; just color them differently and conceal the main portion of their graphics. Same with sandbags & crates; stretch random, default stuff like that to achieve weird effects to get what you want. It's a technique Chakapoko maker and some other brilliant mappers of old once did
