www.greergardens.com in Oregon has it:
10549 ÂCalsap  (ÂCatalga x ÂSapphoÂ) 4', -25°F, ML, 4/3. A very hardy plant with lavender buds that open to white flowers, boldly blotched with burgundy. The smooth, oblong, emerald-green foliage forms a dense cover. This plant won a Best of Show award, so you know it must be a top quality plant. 21-30" (53-76 cm)  $52.95 +S&H

www.rarefindnursery.com in New Jersey has it:
15" to 18" $50 +S&H
18" to 24" $80 +S&H
24" to 30" $125 +S&H

For places closer to you look at:

Here is a link that might be useful: Where to find Rhododendron Calsap in Ohio