can you recommend a place to buy magnets for depotting mac shadows- preferably ones that come with adhesive on the back
You can get them from Ebay.
You can buy strips at Michaels and just cut them to the length you want.
I got mine from ebay but the seller doesn't seem to be selling at the moment (it was this shop in case they come back).
You could buy the sheet with the dots already cut out but it's so much cheaper to buy an A4 sheet and cut them yourself.