Two types of wooden markers you might be interested in:
15mm disks (for example, these on MeepleSource)
Wooden cubes, which frequently come in 8mm, 10mm or 12mm (for example, these on MeepleSource)
This is not an ad for MeepleSource; you can buy these types of parts from a number of online sources.
You may struggle to get a publisher to look at a submission idea for an established game. This is what Hans Im Gluck say about Carcassonne expansion submissions.
We are also interested in ideas for expansions. However, ideas for
expansions are not always unique. Sometimes it happens that we get
similar ideas multiple times and often the author of the game ...