If they have to be "round", then you will limit the number of stamps that you will need. Countries like Tonga and Qatar have issued round stamps somewhat like this. If any stamp with a foil fits your criteria, then there will be plenty of these types of stamps. Many of the former French African and Asian nations have issued gold foil stamps at high face values. Other countries that have done so, off the top of my head include the Netherlands and Jordan. There are others, I'm sure. You can also make your own personalized and valid foil postage stamps at sites like Zazzle. The catalog values are on the high side. Scott does list them. You can also find Cinderella foil stamps from the little islands around Scotland, and of course the Trucial States.
I've always liked these "stamps" despite the "novelty" factor and the "made for collectors" aspects, both of which are undeniable. I'm toying with the idea of trying to put together a complete collection of them. Has anyone ever attempted this or have any ideal how many "stamps" would comprise a complete collection? Are there any really hard-to-find or expensive items? Guess I'll have to peruse the Scott Catalog listings but I would think some of the "sand dunes" issues won't be found there. Anyone happen to have a box of these items and would be interested in giving them a new home?
re: Round Foil "Stamps"
If they have to be "round", then you will limit the number of stamps that you will need. Countries like Tonga and Qatar have issued round stamps somewhat like this. If any stamp with a foil fits your criteria, then there will be plenty of these types of stamps. Many of the former French African and Asian nations have issued gold foil stamps at high face values. Other countries that have done so, off the top of my head include the Netherlands and Jordan. There are others, I'm sure. You can also make your own personalized and valid foil postage stamps at sites like Zazzle. The catalog values are on the high side. Scott does list them. You can also find Cinderella foil stamps from the little islands around Scotland, and of course the Trucial States.