I believe, although I may not be correct, Sumana requested these a while back and has been looking at them... I'm not sure if it covers (new) volunteer contributors or not.
I had provided some numbers, though I'm not sure how helpful they are/have been/will be:
http://lists.wikimedia.org/pipermail/wikitech-l/2012-July/061649.html
Also relevant, the reports for which Sumana had requested help:
https://www.mediawiki.org/wiki/Wikimedia_engineering_report/2012/May https://www.mediawiki.org/wiki/Wikimedia_engineering_report/2012/June https://www.mediawiki.org/wiki/Wikimedia_engineering_report/2012/July (this month, draft)
My message to the list also included a script that could be easily hacked up to look at just about any possible permutation of gerrit searches. I mean really, it's pretty hackish as-is.
As a follow-up, I had made a Python script to do something similar on the GitHub side, but it wasn't as successful or useful in my opinion, since there were only a few additional contributors: http://lists.wikimedia.org/pipermail/wikitech-l/2012-July/061653.html
I hope this can be helpful in some way, at least for substantiating the statements elsewhere that we're still growing :)
Cheers,