Um, wow, you're definetly not going to find one in a junkyard. Why would you think that? First of all, it's a pain in the ass to unbolt off of the car. Second of all, I'd say chances are about 0% that you'll even find one, ignoring the condition it may be in.
Now to be realistic:
www.handaaccessories.com generally has the best prices. I got my kit there for under $500 on sale. Unfortuanetly, they haven't had a sale in almost a year. You can also do a search on
www.parts.com.
I'd advice against getting the wings west kit. You can install both yourself easily, so that isn't an issue. But the WW kit will cost like $600, then you have to get it painted. That paint will not be the quality that Honda uses to paint their underbody kit. Then there's the fact that the WW kit is fiberglass and cracks easily and the Honda kit is plastic. Plus, IMO, the OEM kit looks a lot better and more subtle. OEM kit resale value > WW kit resale value.