I need plans and other drawings of the Imerial War Museum by Daniel Libeskind.

You didn't specify which Imperial War Museum there are several around
the world. Sometimes city hall building departments keep copies of old
drawings. Although on really old buildings like museums these have
usually been lost unless the structure was renovated in the last fifty
years.

Sometimes local Architectural Societies or Colleges / Universities do
What are called measued drawings of existing old buildings. These are
usually done in a bid to save/preserve/ or find new uses for an old
building