There are quite a few synth VST's which support microtuning, among them Native Instrument's FM8, Absynth and Kontakt. Also Omnisphere, u-He Zebra, Xfer Serum, Alchemy, Lounge Lizard (comes with Sonar). Not sure which of them achieve this with .scl files and which require manual twiddling though.
I know this might not be exactly how you're looking to work, but it's worth pointing out that Melodyne has support for microtonal scales too, so you can "correct" audio to fit the scale you want.