Several years ago, an article in the Admin. Sciences Quarterly, June 2002 at 219, explored the diffusion of ISO 9000 Certificates throughout the world. What caught my eye was a chart that showed 34 countries and the amazing number of such Certificates in them as of the end of 1998: 271,847. In the lead were the UK with 58,963; the US had 24,987; Germany 24,055; Italy 19,095; and France and Australia had a few more than 14,000 each.
Given the investment of time and money required to obtain ISO certification, it seems plausible to me that many of the firms that obtained certificates would have at least one in-house lawyer. What I could not determine from the article is whether a company might obtain more than one ISO 9000 Certificate. Either way, we have another data point for estimating the number of legal departments worldwide.