Try this place.

Here is a link that might be useful: greenhouse poly

Home Depot's "clear plastic sheeting" is not really clear but frosted. So I found a great alternative today. The discount store sells clear shower liner. It's a nice size piece, made with heavy plastic, it's crystal clear and already has grommets. And it was less than $4! I plan on making a mini greenhouse over my square foot garden. Used PVC pipe as frame.

Last year I used clear plastic to cover a gap in my green house and found some of the leaves got scorched even in the winter sun. I would suggest using frosted or white plastic instead.