Atlantic Plywood wholesales to several independent lumber yards in Hudson Valley (eg: Williams Lumber). Easy enough to place an order for anything you'd want through one of them.
Williams is a major player in this area, competing with Home Depot and Lowes. They stock pine, red oak, poplar and maple. I never asked about special ordering.
Any of that Murphy hardwood ply that Williams retails is from Atlantic. I think their delivery route from Connecticut to Hudson Valley is twice a week so you’re usually just a day or two out from ordering.
I received an email from Chesapeake Plywood LLC a few minutes ago that they have Baltic Birch in stock right now in thicknesses from 3mm to 40mm
in 5x5, 4x8, 5x10, and 5x12.
I have no connection to them but I am signed up for emails with sales and deals so just passing it on for anyone looking.
They are in Baltimore, MD but deliver to a wide area.
Garnica is good stuff. First time I ever ran a few few sheets was for a buddy he just dropped them off after the first sheet I called him and asked what kind of plywood is this.