As a general rule, the same 'type' or 'group' of clematis will bloom about the same time.
Chrystal Fountain is an early, large flowered type also classified as Group 2-for pruning, so, chances are if you select another large flowered, group 2 clematis they will be more likely to bloom together.
The database is so cool--if you go to the clematis database and search by general characteristics, you can search for large flowered, group 2, and any color or other characteristic you want and see what you think...
http://garden.org/plants/group...
