Is there such a thing as a climbing rose, with no thorns, that blooms profusely all summer long?
Zephirine Drouhin comes to mind right away. An old variety but still a favorite for a lot of reasons, climber, virtually thornless and everblooming.
Nothing blooms profusely all summer long. Hardy repeat bloomers bloom in disernable flushes. Tender repeat bloomers don't necessarily ever put on a really big show. Realistically, the best you can hope for is a big June flush, and sporadic flowers for the rest of the season.
As Bill points out, Zephirine Drouhin is an old favorite (there are two of them
arching over pathways here where people brush past). . .it is also remarkably
shade tolerant! Two other "nearly thornless" climbers out there are "James
Galway" and "Cecile Brunner" . . .
They are wonderful! And, to add to what the others have said, they are fragrant. At least, ours are.
I dearly love Zepherine Drouhin and I have a bunch of them in part shade, but mad_gallica is exactly right about a big June flush and then sporadic blooms all season. Those sporadic blooms can continue into November.
You can always plant a climbing rose and a clematis together. If chosen carefully the clematis can bloom after the rose's main flush and extend the length of time that you have a major bloom happening.