You could do it with the Flag of St David for sure.
As for the Dragon, could you cast a green and white blank and then use a Decal (been looking at this this morning) for the Dragon?
Or cast something like this into a clear resin and turn around it?
Could you cast a green/white transparent resin to match the flag colour?
Sorry, just a brain dump, no idea if any of that would work, and have no intention to start casting my own blanks for a long time!!!
Gav