You could try
www.griggsracing.com . I know they carry them.
Some things to consider is that you can then get lower control arms that are very light, but lose the sway bar mounts. And they are more expensive.
An alternative is to get the adjustable lower control arms, and standard springs.
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Darius Rudis
Roadracer: Home built t-arm/panhard suspension powered by an S-trimmed motor :-)
My Mustang Page