Functional managers are reluctant to provide a project manager with resources for a project because...

Satisfy the functional managers by agreeing with their point of view in order to get the necessary resources.

Advise the functional managers to submit a change request, record the issue in the issue log. and escalate the issue to the project sponsor

Schedule a team meeting to discuss creative ways to incorporate the scope without having to formally submit a scope change request.

Inform the functional managers that the project will produce only what has been approved and project modifications cannot be made at this point.