Is there a way of getting to 3rd elevator on level 3 in Military Base

Due to all of the rubble blocking the way, these areas are not accessible without hacking the game.

If you are very curious, you might try tools such as the savegame editor to hack the game and get into those areas or see what's in those lockers. I don't know if the character editor allows you to modify your location on maps, but you could try it.

Mild spoilers:

You first encounter this area in the original Fallout and can explore the base unhindered, but your actions leave the base in ruins. It is because of this that much of the base is now inaccessible.

Level 3 in the original Fallout:

Level 3 in Fallout 2:

Level 4 in the original Fallout:

Level 4 in Fallout 2:

(images from fallout.wikia.com)