Scott,
You should not have difficulty finding any of those “original” colors. To the best of my knowledge, all are still in production. The reason why I enclosed original with quotes is that nothing will match exactly to what was there when the car was new. Most products today are simply formulated differently and therefore the color value, pattern, texture, etc will vary from what was in your car originally. If you’re doing a complete rehab of the interior, it won’t matter.
As for leather vs MBTex, I would base my choice on how much maintenance you want and how much sunlight will it be subjected to. Both will need periodic cleaning but leather will require more attention. Additionally neither the MBTex and most leathers are not really of the same quality as the originals. The Tex is not quite as durable and most leathers are aniline dyed as opposed to vat dyed as the original material. You can still source it, but it’ll cost you!
Good luck on your project.