"under preparation for" is correct and usable in written English.
You can use it to describe a situation that is in the process of being prepared for. For example, "The staff are working hard to get the store ready for the grand opening, and they are currently under preparation for the event."
"The visit has been under preparation for a long time in cooperation between authorities form Denmark, Australia and Nauru.
Years later, when Winston Churchill — The Valiant Years was under preparation for television, its producers asked Sir Winston who he thought should do the voice of Churchill.
The arrangement, which has been under preparation for weeks, is due to be agreed at a meeting of the quartet today.
sMDT operational and construction experience exists from ATLAS muon spectrometer upgrades which are in progress or under preparation for LHC Phase 1 and 2.
The soft X-ray multi-camera tomography system (XMCTS) is currently under preparation for commissioning and first operation in the next experimental campaign of the Wendelstein 7-X stellarator.
The report by the Justice Department's ethics office has been under preparation for more than five years, and its critique of legal work on interrogations provoked bitter complaints from Attorney General Michael B. Mukasey as he was leaving office as the Bush administration's final attorney general.
Fort St .Jean had been under preparations for an attack from the south ever since Arnold's raid on Fort St .Jean on May 18, in which he captured its small garrison and Lake Champlain's only large military ship.
We have always under-invested in preparation for those kinds of events.
This is currently under investigation, in preparation for updating response products to correct for this droop.
A young woman we know writes: A week or so ago I went out and bought 1500 pesetas (just under $100) in preparation for a trip to Spain.
Meanwhile, attorneys for The Post have taken depositions -- testimony under oath in preparation for a trial -- from the Tavoulareases, Mobil board chairman Rawleigh Warner Jr., Securities and Exchange Commission staff members and others familiar with one aspect of the case or another.
