Here's a good list:
trusted aftermarket sites???
As for the leveling struts/shocks, you have to remove the old ones. Compress the spring off and install it on the Bilsteins. Then just reverse the process.
Getting the spring off is the most difficult part because most don't have access to a spring compressor. I just took them down to a tire shop and used their spring compressor, but you can rent/borrow the handheld version from places like AutoZone.