Lots of sources if you Google 'seed starting supplies'. Novosel Enterprises is one source that is frequently recommended every time this question comes up. But it is just one of many sources that offers all sorts of flats, trays, plug flats, transplant pots, humidity domes, etc., etc.

Dave

Tek Supply, Growers Supply, Agri Supply, Greenhouse Megastore, Johnny's seeds, are some others.

Some garden nurseries throw many of their trays and containers in their dumpsters. A little dumpster diving and elbow grease can make a good collection of trays and containers.

I found my bottom flat tray at a local nursery. They also sold the individual six or four packs. I save them from year to year. When ever I buy a six pack of flowers (which I always wind up buying a few), I am very careful when removing the plants so I can re-use them. I just soak them all in bleach water in the beginning of the growing season to kill any germs. The other place you may want to try is fish markets. The one my mother used to work at years ago received their fish in these clear shallow plastic containers that had lids. They would also be great for winter sowing.

I found my bottom flat tray at a local nursery. They also sold the individual six or four packs. I save them from year to year. When ever I buy a six pack of flowers (which I always wind up buying a few), I am very careful when removing the plants so I can re-use them. I just soak them all in bleach water in the beginning of the growing season to kill any germs. The other place you may want to try is fish markets. The one my mother used to work at years ago received their fish in these clear shallow plastic containers that had lids. They would also be great for winter sowing.

Other than the hundreds (yup) of pots I recycle, and be basic Burbee trays I've saved, I ordered 200 4" round pots and 10x 144 cell plug trays from Harrisseeds.com. I also ordered 1 pt of organic fertilizer to experiment with, and a 4way meter just for haha's.