Re: Fret marker dots
Plastic rod is often what is used. Its either 2mm or 2.5mm thick. Drill hole, insert, clip then level sand.
You need a luthier type store, LMII, Stewmac etc for the 'official' stuff. But if you can find something else convenient then I don't think it matters
You can also perhaps use a glue/sawdust mix and jam that into any size hole you want, or even a builders putty.....which is not too dissimilar to Fender Clay dots