3 links have been added on this idea.
  1. Odd that you can’t get the grid you would need. These guys suggest making individual 1 foot square tiles then sticking them together, which doesn’t sound as easy as just sticking the grid down the filling it all in.

  2. There are lots of tips on how to make your own here https://www.prettypurpledoor.com/penny-floor-faq/ but nothing about where to buy a mesh or grid that you just pop the coins in and cover with resin/fixant. Anyone? or has the roll of mesh stuff not been invented.