I don't need to find anything, I already know an essential fact: namely, that the organisational structures of the Japanese keiretsu is actually fairly unique when compared to Anglo-American or European corporate structures, relying on an heavily interconnected network of suppliers that the lead companies slowly bind into their business models until they cannot throw off their overlord, shaking off the costs to their individual specialist suppliers and keeping the profit of selling the finally assembled products for themselves.
Meanwhile, the EITC was heavily dependent on private investment and share ownership/buying/selling to raise capital, used trade and later violence to break open previously inaccessible markets for their products, was heavily concerned with acquiring "specie" (i.e. precious metals) due to the silver/gold standard, focussed on trading already manufactured goods (spice, porcelain, tea, etc.) and used a network of independent contractors to circumvent restrictions on their activity.
Like, sure, you can probably compare the EITC and the Japanese keiretsu and notice some similarities. They are also separated by, what, a century, two world wars, and several revolutions in production management and technology? At minimum.
I have a hard time believing the claim that the idea of the megacorporation in the cyberpunk genre is specifically influenced by the idea of the EITC. I think the influences of the popular culture, and more importantly the popular impressions and popular fears of the time in the 1970s/80s, were far more important.