Where to buy polystyrene hatching egg boxes in bulk?

Im wondering where people get their hatching egg boxes from?

Thanks

I was thinking its nearly the season to be selling hatching eggs on ebay so was going to start giving it a go I do see the egg boxes on ebay but wondered where the people on ebay get them from? Im not sure commercial is the word, more so just selling my eggs for hatching rather than eating as you know the price can be 5 times as much but I will only be able to supply about a dozen or so eggs a week so shall run 2 auctions a week if all goes to plan. Its basically to get some of the costs back from the hatching eggs I bought at the beginning of last year and to offset the cost of feed and worming meds.

Ebay seems to have them around £1 a box, I was hoping to dig around and find them for 50p a box.