It's true that gearbox manufacture is focused on two main suppliers, Winergy and Hansen (30% market share), which is owned by Suzlon.  For these companies to remain profitable, they will still need to supply the owners' competition, at least into the mid-term.  Supply contracts remain in place to the competition.  But over the past two years other gearbox manufacturers are both increasing market share and ramping up production.

Siemens stated upon the purchase that they were interested in the parent, and that they would not interfere with the core business.  I wouldn't want my gearbox load data in the hands of the competition, however.  But even they source elsewhere as well.

Many turbine manufacturers source gearboxes from different competing suppliers.  Siemens itself sources from Hansen.  Suzlon didn't source from the company it bought, Hansen, rather Winergy and the small German company Jahnel Kestermann, though that will begin to change soon.  Nordex has three suppliers including a subsidiary of Bosche Rexroth for their new differential gearbox.  Vestas sources from four companies, including Finnish Moventus.  Gamesa sources from five companies, as does GE, though GE is slowly increasing production at another GE subsidiary.  REpower sources from three companies, and a fourth, RENK (new to the industry) provides only for the giant 5M.

New production capacity is beginning to come online in China and India (where else?), and almost everyone in Europe is adding capacity.

But nearly all large gears (main shaft) come from FAG or SKF.  And there's the rub.

"Life shrinks or expands in proportion to one's courage." - Anaïs Nin