We ran into the same thing when we were facing an imposition upgrade last summer. We were on Metrix 2013 standalone (single license), but Metrix has since been absorbed into EFI, and standalone pricing was next to impossible to obtain (and pretty pricy once we finally got a quote).
Here are some options we explored (note--some of these stand alone pretty well, but may or may not work well for your shop, and some others only really sold as part of a larger prepress installation):
Agfa Apogee Impose
Devalipi Imposition Studio
Heidelberg Signa Station
Tilia Labs Phoenix
Ultimate ImpoStrip
Hope this helps!