Clematis On The Web has an advanced search option. Choose group III from the 'Pruning group' drop-down menu. You can also add color option to your search.

Prince Charles and Betty Corning are lavender
Rouge Cardinal is magenta as is Earnest Markham
Madame Julia Corrovan is red and so is Kermesina
Huldine and Alba Luxurians are white

In Integrifolias like Arabella, Gazelle is white, Alionushka is pink/lavender, Pangbourne Pink is too.

Clematis texensis Duchess of Albany is pink with a red bar, tulip shaped
c. texensis 'Princess Diana' is shades of pink, tulip shaped
c. texensis 'Gravetye Beauty' is bright red, tulip shaped
'Comtesse de Bouchaud' is a large flowering pink
'Hagley' is pink with ruffled edges
'Pink Fantasy' is pink
'Ville de Lyon' red
'Recta' white

I've checked COTW a few times. I actually popped on there this morning after I posted and I think I need to remember to LOOK before I post.

Went BACK to the store today and bought Rouge Cardinal and Comtesse de Bouchaud. They also had Hagley. I think I might get it next time I'm in town.

This is so sad! I'm going to quadruple my # of clems in one month!!! It's ok though ;) I'm getting a jump start on landscaping the house we're building.

You could also go through the nurseries. They should list zones and pruning groups, or list group 3 as summer blooming.
Brushwood
Joy Creek
Garden Crossings
Donahue's
SilverStar Vinery
etc...