Find a joinery shop that can laminate thin birch ply to a solid core door. Very common to skin and lip blanks with hardwood veneer. You want the best finish grade ply tho to avoid patches / knots etc
This - two sheets of decent mm birch ply (quite spenny these days) glued/laminated and then cut to your side would do it. i've used balls pond joinery for a few sheets of ply cut up before and they've been pretty good.
(potentially useless recommendation depending where you are)
Find a joinery shop that can laminate thin birch ply to a solid core door. Very common to skin and lip blanks with hardwood veneer. You want the best finish grade ply tho to avoid patches / knots etc