SADLY, unless you are using a BS1088(or similar) rated MARINE PLYWOOD you wont likely be able to secure voidless or even near voidless plywood from another/any supplier
having a method to fill the discovered voids will likely just have to suffice
when i discover a void i try to orient the edge in question to vertical and let gravity aid in the filling w/ a slightly thickened EPOXY slurry which sometimes takes A WHILE...
SOME are saying TITE BOND II or III will achieve the same goal butt takes more time to fully cure
i am currently experimenting w/ TITE BOND III butt the jury is and will still be out for several months due to the time it takes for it to cure to a sandable state w/o gumming the grit
the POX usually cures to sandable within 24-48± hours
filling known accessable voids, up front, is in your best interest