Where is the best place to purchase boxes for tiered cakes.
What kind of boxes are you looking for? Specially made to transport tiered cakes? I've seen a few like that, but I just use heavy cardboard shipping boxes from Wal-Mart. Around here they sell they super cheap...I can buy an 18x18x24 for less than $2! I lay the box flat and cut off the top 2-3 inches in order to make a two piece box and lid.
I assemble the box and tape all the flaps securely in place with good packing tape (I love Gorilla brand tape).
I then cut one side from top to bottom on both the left and right sides so that the front of the box folds down forward (think of a castle's draw bridge).
I place my well-chilled cake in the box on a piece of rubber non-slip mat, then close the flap up and tape in place, then add the "lid" I made from the portion I cut off the top....box is ready to go!
I've transported up to 5 tiers fully assembled as far as 3 hours away an never had a problem!
and they are reusable -- don't forget to leave a couple regular cake boxes for any possible leftovers -