I can't see any listed nursery offering them in north America (not all nurseries list their wares on helmefind). It looks like Perle von Heidelberg may be lost. I think your best bet is to contact a Heritage Roses group in Canada or northern USA.

For other roses: click on Plants - search/lookup in the left menu, then type in the name of the rose you want and click on Search. If more than one rose with that name appears on a list, click on the one you think most likely. When you get to the page for the rose, click on the Buy From tab at the top right of the page.