Expanded polystyrene (EPS) seed trays

Does anybody know if you can buy expanded polystyrene module trays if you're not a nursery or suchlike placing a huge order? I've had a good look around the internet and can't find anybody selling them in small quantities for the home gardener - only the actual manufacturers. I thought they might be good in my extremely chilly greenhouse as they offer some insulation.

Alas, there are no fish shops around here. I guess I could try my local T*scos? I was really looking for the actual seed trays with modules though. It just seems odd that you can't buy them as all plants from garden centres and nurseries are sold in them and the older gardening books always assume you can get them. 

Thanks Poppies! I've had a look and they sell packs of 100 for £28. I don't think I need quite that many  Still, that's the nearest I've got so far and gives me hope that they must be out there somewhere in smaller quantities!