Where can I buy heavy boxes (corrugated) to ship cheesecakes and cakes.

Check your local yellow pages (unless you don't live anywhere near a big city). Most paper companies carry a full line of "baking" paper products and of course boxes. Sometimes the person that answers the phone isn't the most helpful (they take orders but don't know the product line), ask for a sales rep. and tell them what you are looking for.

Some of the larger companies have better prices but don't really want to deal with Mom & Pop type of buyers. So they might not rush to handle your order but stick with it. Unless your meeting their min. you'll probably want to pick it up your-self (mention you'll pay in cash and sometimes they drop taxes)....delivery charges can add up.