Thanks to Dave Bacon, the link (available via a few clicks starting at the About menu item on NBER's homepage) to the 2010 financials summary page of their annual report (if you follow the link, go to the bottom of the page and click).  Trying to find the full report online has proven bootless...so far this is what I've turned up.

However as I pointed out in comments on my earlier post, responding to the summary fiscal 2010 financials Dave provided, the vast majority of their money---32.4 million out of revenue of 39 million---is coming from current grants.  Given this, the $10 million from four right-wing foundations over 16 years, detailed by SourceWatch, is extremely unlikely to represent a signficant fraction of their funding during that period although without access to financial statements, who knows.

Since I've gone this far, I suppose I should probably just ask NBER for the info!