Here is a photo of two desks, one on top of the other.

I think the section for the drawers would be ideal as nesting boxes. We have the drawers as well so perhaps you could put one in the bottom to stop the bedding falling out.
I will pm you the location. You could collect any time up to the end of August. If I know you (or any other isher) wants some, I will put them to one side.
Cheers
Zoe