There's been a bit of work on pulling apart the standard ROM. But how far that's got I don't know. Without knowing whats what it's just a bunch of binary. There are quite a few in the know though, the aftermarket chip manufacturers. But they keep the info close to thier chests i would think.
I've got a couple of maps here for DTA on a 1.6 16V if you want. On standardish sort of map from Velos, and one silly power TB'ed grasstrack corsa one.