Just saw this today at a visit to the Summit website. Appears that Summit is now offering stock height and lowering springs for the Challenger! Not sure what the spring rates are or where the manufacturing location is, but it might be worth a try for someone looking to replace their leaf springs. We all know that the Mopar springs are made in Mexico already, and tend to sag pretty low after install (although that works out if your going for that low look).
Lowering springs
http://www.summitracing.com/parts/SUM-7074CH-2/Stock height
http://www.summitracing.com/parts/SUM-7074CH/Both are listed as 5 spring pack 57" rear leafs.