I saw an effect performed with a long ribbon that was placed inside a chain of three boxes. The boxes were moved apart and the ribbon was cut. The boxes were pushed back together. The ribbon was pulled out and was restored...
Does anyone know the name of the effect and where can I buy it?

Never heard of it nor seen it. My question to you is, why would you want to spend money on some prop that is less Magical than doing the same effect using just the rope or ribbon and your bare hands?
There are lot's of excellent props available that enhance your Magic but it seems to me that the prop that you are looking for can only diminish your Magic.
Just my personal opinion. Best of luck finding your prop.
Iven