As a source for cheap or free big pots, contact landscape companies. The one that gave me my pots had just finished a huge project and was going to have to pay to recycle the pots. They were happy to give me as many as I wanted free and even cleaned them up for me.
As for cutting the roses back, it's probably best to plan on cutting them back because the root ball will be smaller and the roots will be less efficient when you've dug them up and moved them making it harder to support the top growth. Don't worry, the roses will come back just fine.
Lyn
