I don't want to sound negative, but save your self the time and don't bother.
As a LQS owner who spends 10's of thousands of dollars with vendors every year, we can't get vendors/manufacturers to donate fabric or batting for charity projects. Truth be told, the are overwhelmed by requests and cannot possibly donate to everyone who asks.
We have a small group of quilters who work on charity projects all year long. The majority of the fabric comes out of their stashes or from other customers who donate to the cause.
Check with your local guilds, put an ad in the paper, or on Facebook marketplace seeking donations. You'll probably get better results.
Good luck!