Felix – I don’t understand why your Owners Corporation (O/C) would be bothered with a report commissioned by an Owner, when you say that the O/C itself commissioned its own report and engaged the services of a consultant to examine the very same magnesite problem.
However if your O/C is after just corroboration, IF the payment of the Owner’s costs was (as it should have been) made on the basis of an Invoice provided by the Engineer engaged by that Owner, then (as a Chartered Engineer myself) I can advise that it’s customary for professional courtesy to be afforded to the extent that the former would, as a minimum, share his/her then findings with the O/C’s Engineer.
So perhaps you’ll need to arrange that audit, and hope that irrespective of to whom payment was made, there’s a record of an Invoice made out to somebody by that Structural Engineer so that you can by-pass their uncooperative Client.