Back in the 1993 when WTBTS of Pennsylvania registered as an overseas branch in Britain, they were required to file financial statements. They closed their overseas branch in 1999. However, in doing this they left a trail of financial statements and internal operating structures that have since been obtained and published. These can be downloaded from JWLEAKS:
http://jwleaks.org/watchtower/
A full set of current financial documents and historical documents for WTBTS of Britain, International Bible Students Association (IBSA), and Euopean Association of Jehovah's Christian Witnesses can also be downloaded from JWLEAKS: