There's the dogs available and several shops including axminster ect... Also ebay and amazon.
The only issue you may find is that they aren't all the same diameter, some are 19.90mm and some are 20mm so depending on the manafacturer of the MFT depends on the hole size.
You may be unlucky and find the dogs you buy may be sloppy in the holes.
I was on the bench dogs site the other night and the prices are pretty expensive for what they are selling, especially the flag stops.