I see you are from Raleigh. Here's a few ideas.
Be prepared to open your wallet - this is not cheap.
Here's one source in Raleigh I know of - Capitol City Lumber on Beryl Rd near fairgrounds. Website seems to indicate choices in stock - call ahead to be certain, (you don't mention thickness requirements) Walnut Plywood - Capitol City Lumber
A bit further out is the Hardwood Store in Gibsonville - an advertiser and supporter of NCWW - see ad on right side of screen. Also have choices in thickness. I'd also call there before I drive out. Great place to visit if you have not been there! Hardwood Plywood | The Hardwood Store
Edit - And Mitch posted ahead of me while I was typing and finding links.
I would budget $110 to $150 per sheet depending on face grade and core material.
At most suppliers you will need to specify face grading; plain slice vs rotary and AA, AB, AC, or BC
Plus you will need to specify core specs such as MDF, veneer, lumber, particle, MDF/veneer, or high denisity
If you need a lot of premium plywood, it might be worth checking Atlantic Veneer in Beaufort, NC (the town, not the county). It manufactures plywood and they have an outlet store. Haven't been there for a long time but they used to be able to supply at a pretty good price, and at that time (10 years ago?) they would custom make sheets in many species with a six sheet minimum, either radial or sliced veneer. Moehrings owns them now, a German firm. Check the outlet store/ email: email@example.com for current info.