Hello Ccrewz try reading this

http://www.lathamtimber.co.uk/icmedi...%20Plywood.pdf

Plywood comes in different grades, you can get crap quality or amazing quality plywood from just about any county that grows wood, it is the grade that counts. Obviously the higher the grade the more expensive it is...

If this stuff is going in a hospital or somewhere that will be doing some hardcore cleaning you might want to get exterior grade so it doesn't start to delaminate when the cleaners start scrubbing it. (exterior grade plywood uses a water resistant glue, not as good as marine grade glue but better than interior grade glue)

As you already have plans and a cnc machine it might be worth spending a couple of days on the phone ringing around all the timber yards and cabinet makers you can find and ask them to keep a pile of good sized offcuts for you or to give you a free sheets for free in exchange for engraving their logo somewhere.

If you do have a problem getting hold of plywood you can always consider using a plastic laminate or veneer something like formica/melamine or even fablon on top of cheapo plywood/chipboard/mdf.

Take a look here:

d-c-fix Sticky Back Plastic - Birch - 67.5 x 2m from Homebase.co.uk

Cheap, waterproof, easy to clean, comes in a million different designs and you can stick it on top of just about any old crap ...