Possibly Jun too? I know they make some pretty aggressive cams, i'd think they'd make springs and retainers to go with the cams, but i'm not sure of that. the JWT's are going to be your best bet. If you don't mind me asking, what cams are you going to be running to require these parts?
Ferrea and Manley make Stainless Steel valves for the US Spec Head *only* not the DET! Ferrea also carries valves springs and retainers. JWT also carries valves springs and retainers. HKS, Greddy, Tomei, APEXi, JUN and Toda all make valves springs and cams for the SR20. Comp Cams (Zex) makes springs and retainers for the SR20 along with cams!