Ecklers has them;
http://www.ecklerscorvette.com/corve...1969-1996.html
Thing is with a lot of these little parts, you need to look at other models that tend to get over-restored. Camaro catalogs are another good source for little bits that is used cross platform, but not necessarily listed for other platforms. I have a Nova, lots of little bits are the same as on a Camaro, but the catalogs only have the parts listed for the Camaro but not in their Nova catalogs. Thats why I suggested a local UK shop that caters to "popular" American Cars.
Poking around ecklers some more;
http://www.ecklerschevelle.com/cheve...1967-1972.html
Different Price. Same part functionally and interchangably (they may actually source from two different places though, somebody is not doing a complete cross checking of parts. Might change if they pay attention to search terms used, and hits from links to specific parts. I see they also list the part for Camaro, but not Firebird).
And El Camino they list separate left and right spring at a buck 99 each, but not a pair.
Things that make you go hmmmm.... I also think this is the first time I have seen a "corvette" part cheaper. And if it is marketing driving pricing levels, El Camino guys must be easier to get a few more bucks out of.
Alex.