Hamaguri was a Japanese investment consortia that was one of the main contributors to International Genetic Technologies, Inc. of Palo Alto, CA. Little to nothing is known about the investment firm, but it is assumed they owned a high amount of general stock in InGen.
According to the novel, the Japanese were the only investors patient enough to wait five years before return-capital. It is also stated that they traditionally shunned publicity and had dealt a serious financial blow.
An unused quote from Trespasser states that Hammond went to Hamaguri and Densaka in 1979 to ask for funding. In the end, the Japanese were the only investors patient enough for his eight-year plan.