Here are a couple suggestions listed in order of height and then hardiness:

'Refrain' [Vittatum x Miyagino], White, Flower 1 3/4' to 2" across, hose-in-hose, white suffused with brilliant to light purplish pink and a few deep purplish pink stripes, conspicuous vivid purplish red blotch. Inflorescence 1-3 flowered, Early Midseason, 7 ft. tall in 10 years, -15F (-26°C), Upright habit.

'Amoenum' [Obtusum clone], Red, Flower funnel-shaped, 7/8" across, hose-in-hose, vivid purplish-red. Inflorescence 2-3 flowered, Midseason, 7 ft. tall in 10 years, only 0°F (-18°C), Leaves elliptic to elliptic-obovate, mid green. Spreading, very dense growth habit. Grows wider than tall.

'Palestrina or Wilhelmina Vuyk' [kaempferi hybrid x J.C. van Tol], White, Flower broadly funnel-campanulate, 2" across, white with dorsal throat spotted green. Inflorescence 2-3 flowered, Early Midseason, 6 ft. in 10 Yrs, -15°F (-26°C), Leaves semi-evergreen, elliptic, 1 1/8" long, hairy. Upright growth habit.

'Geisha' [Vittatum x Miyagino], White, Flower 1 1/2" to 2 1/2" across, white, flaked and striped moderate reddish purple and a pale greenish-yellow blotch. Inflorescence 2-4 flowered, Early Midseason, 6 ft. in 10 Yrs, -10°F (-23°C), Spreading habit.

'Snow' [unknown], White, Flower openly funnel-shaped, 1 3/4" across, single, hose-in-hose, white with a faint greenish-yellow blotch. [1-1/2" across], Early, 6 ft. in 10 Yrs, -10°F (-23°C), Leaves glossy, dark green. Upright, spreading habit.

'Dayspring' [Vittatum x Marta], Pink, Flower openly funnel-shaped, 1 3/4" to 2" across, white center shading to light purplish-pink at edges and a greenish-yellow blotch. Inflorescence 2-4 flowered, Early to Early Midseason, 6 ft. in 10 Yrs, -5°F (-21°C), Leaves obovate. Broad, spreading habit.

'Fashion' [indicum x Momozono], Pink , Flower single, 2" across, hose-in-hose, deep pink with a purplish-red blotch and dark red anthers. Inflorescence 2-4 flowered, Early Midseason, 6 ft. in 10 Yrs, -5°F (-21°C), Erect habit.

'Festive' [Vittatum x Ho-oden], White , Flower openly funnel-shaped, single, 2" to 2 1/2" across, white spotted, flecked and occasionally striped strong to vivid purplish red. Inflorescence 2-4 flowered, Early Midseason, 6 ft. in 10 Yrs, -5°F (-21°C), Erect, spreading habit.

'Mother's Day' [Professeur Wolters x Hinodegiri], Red, Flower openly funnel-shaped, 2" across, hose-in-hose to semi double, strong red with faint deep red dorsal spotting. Inflorescence 2-3 flowered, Early Midseason, 6 ft. in 10 Yrs, -5°F (-21°C), Leaves 1" to 1 1/8" long, bright green, tinged red. Compact, spreading habit.

'Seneca' [Vittatum x Alice], Purple, Flower open-faced, 3" to 3 1/2" across, strong reddish purple with a white base and a blotch made up of clearly defined marks between vivid and strong red. Inflorescence 2-3 flowered, Early Midseason, 6 ft. in 10 Yrs, -5°F (-21°C), Very erect habit with ascending branches.

'Cavalier' [Kagaribi x Hinodegiri], Pink, Flower openly funnel-shaped, 1 1/2" to 1 3/4" across, deep yellowish-pink with orange undertones. Inflorescence 2-4 flowered, Early, 6 ft. in 10 Yrs, 0°F (-18°C), Leaves elliptic, acute apex, cuneate base, dark green. Erect, dense, bushy habit.

'Delaware Valley White' [mucronatum hybrid], White, Flower 2 1/2" across, white, unmarked, Early Midseason, 6 ft. in 10 Yrs, 0°F (-18°C), Open, spreading habit.

'Delos' [Vittatum x Waraigishi], Pink, Flower about 2 1/2" across, double, light purplish pink, unmarked. Inflorescence 2-4 flowered. Occasional second bloom in fall, Midseason, 6 ft. in 10 Yrs, 0°F (-18°C), Erect to spreading habit, somewhat overarching.

I don't know where you can find these. Delaware Valley White should be easy to find. The others aren't too common since most of the taller azaleas don't sell to well. People that don't want a tall plant call them lanky.