Same here. Unfortunately there does not seem to be any freely accessible FCOM on the Internet yet, otherwise it would be trivial (although time-consuming) to just turn the performance tables into a PFPX profile. I don't have high hopes that anything changes about that situation. Limited data is provided with the addon documentation but I doubt it's sufficient to produce a reasonably accurate PFPX profile (dataset looks much too small; haven't tried it yet, though).
It's a repeating problem with other addons as well - either there's no data at all or only for a wrong engine type or aircraft variant. For example, the Felis B742 has that problem as well (FCOMs exist but performance data is extremely rare with incomplete data for the exact combination of type and engine) but at least the profile that has been posted matches closely enough that adding some bias comes up with reasonable numbers that aren't completely off. Searching with Google for the Challenger 6 series (not even limited to the 650) nothing has turned up at all so far in my searches. I guess the chance of somebody leaking original documents to the Internet is much lower for a business jet (company-specific documents? fewer pilots) than it is for a standard airliner ("mass-product", minimal changes within the same aircraft family, lots of pilots).
I already thought that maybe it would be better to write some sort of plugin/script that simply generates performance data tables by flying the simulator addon (all automated, basically a "test pilot drone" - let it run for 2 days going through all possible weather conditions and airport elevations and you should have a ton of data to feed into PFPX). Unfortunately, I'm not aware of such a tool yet.
I seriously wonder where SimBrief gets their performance data from. I don't think aircraft manufacturers are happily providing the flightsim community with their data (at least not unless you have a better reason than simming to receive such documents). Is there some other (official, generally available) source for performance documentation which I'm not aware of yet? Maybe some portal that just requires a login (and thus doesn't turn up in Google searches) but where basically everyone is allowed to register for an account?