I asked the U of M students who were operating the big bubble blowing stall for the recipe.
Here you can see the size of the black plastic trays they used, which they filled with a mixture of blue Dawn washing up liquid and water, with some glycerine which makes the bubbles stable for a little longer. In the trays they used, they had about three quarters of a bottle of Dawn, then filled the trays with water, so it is about one fifth Dawn to four fifths water.
The giant wands are made from a cane, then attach metal wire coat hangers moulded into the shape you want, wrapped with cut up strips of tee-shirt!