Springs typically last a very long time, if not forever, and when they go bad, they just snap. How many miles do you have? try the struts/shocks first, you will be surprised how much more of the original ride you retain. If you feel springs are needed at that point, you can go down that road later.
As far as places for Bilstein HD's, I got mine from fastlane, best price i could find, Phil is a great help, and we try and support him as much as possible.
Below is a great thread i started on the HD dilemma, plus installation, check it out.
http://www.peachparts.com/shopforum/showthread.php?threadid=78393&highlight=bilstein+HDs+raise
FQ