Stage Show-Only Kamen Riders

Kamen Rider Alpha (2003)
In the story of the Kamen Rider 555 stageshow, the Alpha suit was used by a female character. Pictures avaliable here in this Japanese site.

Kamen Rider Beta (2003)
In the Kamen Rider 555 stage show.

Kamen Rider Gamma (2003)
In the Kamen Rider 555 stage show.

Kamen Rider Kyoki (2005)
Kyosuke Kiriya also briefly transformed on the show into what was called Transformed Kyosuke by the Hibiki production crew. In the stage shows of Kamen Rider Hibiki, this form is dubbed Kamen Rider Kyoki which means "Strong Demon".

Kamen Rider Riki (2005)
In stageshow for Kamen Rider Hibiki.

Kamen Rider Mujaki (2005)
A female Oni Kamen Rider as age 23, a human with Makamou blood in her veins who brainwashed Jaki into being her slave. Mujaki use a microphone as her weapon and her name means "Illusion Snake Demon" and is synonymous with innocence. Her headress reminds me of villainess Tsuetsue from Gaoranger (Toxica of Wild Force).

Kamen Rider Jaki (2005)
The older brother of Kagayaki. He is 25 years old and was brainwashed by Mujaki into becoming her slave. Jaki use a saber as his weapon and his name means "Snake Demon".

No Pictures:
Kamen Rider Kagayaki
A Oni whose weapon is a flute and lamp combination. His motif is green and he is the mortal enemy of Mujaki. 22 years old. His name means "Radiant Demon".

Kamen Rider Yūki
An Taiko Oni who appears in a dream to Kamen Rider Kagayaki. He is from the future in a time where the Makamo, lead by Mujaki have defeated most of the Oni Kamen Riders. His name means "Brave Demon".

Pictures from this Japanese Site.