Daniel Golden's book Spy Schools highlights a few interesting anecdotes about how think tanks are often used by foreign and domestic intelligence service.
Golden, citing a former CIA operative, notes that every single day, intelligence services around the world work conferences, sponsor conferences, and look for ways to get people to conferences in order to help collect information and recruit spies.
The book says that the "graybeard" of "CIA concealment conferences" is the RAND Corporation. The think tank holds a number of conferences each year, often under non-disclosure agreements with intelligence agencies, according to the book.
It also notes that Barbara Walter, a University of California, San Diego political scientist, gives unpaid presentations on her specialty, civil wars, at think tanks fronting for the CIA.
Dr. Walters' UCSD biography lists a number of policy briefings she has given, including at think tanks such as RAND, the Atlantic Council, and Council on Foreign Relations (CFR).
Funders of RAND include the Office of the Director of National Intelligence (ODNI).
Also, as Think Tank Watch has reported, think tanks, including RAND, abound with former spies.