They seem to be popping up everywhere these days. I even see them at the dollar stores. Check all the big box hardware stores in your area and Walmart, Kmart, etc. Places like Farm&Fleet too if you have those in your area. Don't forget local nurseries. You may have to wait a few more weeks before most stores are stocking them. Also try online gardening supplies or online sites of the above stores. HTH

Since the dome is useless after the seedlings emerge, I don't use them any more. I plant in a tray or pots and cover it with a clear plastic bag. As soon as I see sprouts, I trash the bag and put the container under a good light. Works for me.