If I were you I would go to Pickerings website and do a search for Z4 hardy roses.
Since they're Canadian based, they will have more of the roses you need for Z4.
Plus their roses are on virus free understock and they have some own root roses as well
now but I've never had any issues with their grafted roses which I prefer to fall plant even well into November.
I would not buy roses (bareroot or potted) from seed catalog type vendors.
Here's an article I wrote on Hardy Roses.
Hope this helps. Good luck!
http://garden.org/ideas/view/C...
