I think that Ura Zelda ended up being Master Quest, and Majora's Mask.
If I remember correcty Ura Zelda was originally meant to be OOT with new content, and harder dungeons.
At some point Nintendo decided to make the new content into a new game(Majora's Mask), and the harder dungeons become Master Quest.
If my theory is right, then Ura Zelda probably does not exist in it's original form as a playable game.
This would not be the first time that Nintendo did something like this, remember Super Mario 128?
Parts of Super Mario 128 have been used in other games like Pikmin, and Super Mario Galaxy.
No... Majora's mask started as an entirely new project called Zelda Gaiden, and ended up being MM.
Ura Zelda was an enhanced OoT, I truly believe that we lost tons of content.
ABout MM, here's the article:
Development
Following the release of Link's Awakening in 1993, fans waited five years for Ocarina of Time, the active development of which took four years. By re-using the game engine and graphics from Ocarina of Time, a smaller team required only two years to finish Majora's Mask. According to director Eiji Aonuma, they were "faced with the very difficult question of just what kind of game could follow Ocarina of Time and its worldwide sales of seven million units", and as a solution, came up with the three-day system to "make the game data more compact while still providing deep gameplay".[15]
Majora's Mask first appeared in the media in May 1999, when Famitsu stated that a long-planned Zelda expansion for the 64DD was underway in Japan. This project was tentatively titled "Ura Zelda" ("ura" translates roughly to "hidden" or "behind"). This expansion would take Ocarina of Time and alter the level designs, similar to how the "second quest" expanded upon of the original Legend of Zelda.[16] In June, Nintendo announced that "Zelda: Gaiden", which roughly translates to "Zelda: Side Story", would appear as a playable demo at the Nintendo Space World exhibition on August 27, 1999.[17] The media assumed that Zelda: Gaiden was the new working title for Ura Zelda.[17]
Screenshots of Zelda: Gaiden released in August 1999 show unmistakable elements of the final version of Majora's Mask, such as the large clock that dominates the center of Clock Town, the timer at the bottom of the screen, and the Goron Mask.[18] Story and gameplay details revealed later that month show that the story concept as well as the use of transformation masks were already in place.[19]
That same month, Miyamoto confirmed in a Famitsu article that Ura Zelda and Zelda: Gaiden were separate projects.[20] It was unclear if Zelda: Gaiden was an offshoot of Ura Zelda or if the two were always separate. Ura Zelda became Ocarina of Time Master Quest outside Japan, and was released on a bonus disc for the GameCube which was given to those who pre-ordered The Wind Waker in the US and bundled with the GameCube game in Europe. The Nintendo 64 release was canceled due to the failure of the Nintendo 64DD in Japan.
In November, Nintendo announced a "Holiday 2000" release date for Zelda: Gaiden.[21] By March 2000, what ultimately became the final titles were announced: Zelda no Densetsu Mujura no Kamen in Japan and The Legend of Zelda: Majora's Mask elsewhere.[22]
Source: Wikipedia