There's one here, but it's not complete and has MD-only data mixed in.
http://forums.studentdoctor.net/showthread.php?t=918777
Here are some data on MD/PhD applicants/matriculants:
https://www.aamc.org/download/321548/data/2012factstable35.pdf
To summarize that data from 2012:
Mean applicant MCAT=31.2
Range applicant MCAT=4-43
Mean matriculant MCAT=34.5
Range matriculant MCAT=23-43
Mean applicant GPA=3.6
Range applicant GPA=2.2-4.0
Mean matriculant GPA=3.8
Range matriculant GPA=2.9-4.0
Keep in mind these include every MD/PhD program in the country. I would say that ~70% of MD/PhD students are at MSTPs, which are more competitive.
At the tippy top, UCSF and Hopkins had put up on their websites that their matriculant MD/PhD class both had averages at 3.9/37-38. I would be confident in saying that the average MCAT at both those places has risen a point since they put those numbers up.
For a perspective of other programs: UNC has on their website that their average of accepted students is 3.75/35. I would say MSTPs not in the top-15 would have numbers similar to this give-or-take 0.1 grade points and 2 MCAT points.