Southeast USA marine plywood source?

[Dirtmechanic]

Hard to find marine plywood near Birmingham Al or as usual I have no idea what the correct search terms are or even a concept of marine plywood having a different distribution channel from a Big Box. In this instance I need maybe 3 sheets to rebuild one of those 600 dollar vermont garden carts because damn they are good. They state it is 1/2“ exterior grade but Since my Grandpa had me using one at age 14 andlater I paid 400 for my own I can tell you it is not normal exterior grade panel.