Just in case you don't see it in the GD thread, mystikmind may have answered your question.

https://www.gog.com/forum/general/what_is_closest_planet_where_i_can_find_endurium/post23

Is this for Starflight2? if so, can you give me the coordinates of Gallious or any other planet containing Endurium

I may call things by the wrong name but the last time I played the game was back when it first came out. I don't know about Starfflt 2 but in the frist one you can make endurium. Go to a planet that's rich in titanium and magnesium then mine both but don't return to your ship, I think there's one really close to the starport but I don't remember which one. When in your shuttle/mining craft pick up 50 units of magnesium and 50 units of titanium or as much as you can get of each. Now drop both minerals on the ground and this will mix then into endurium. You now have to move your shuttle one space in any direction to complete the process. On the ground you will now see endurium for you to pick up although I can't remember what the the numbers you need to get the maximum amount of endurium when mixing but you can figure that out yourself. This method of getting endurium is really useful if you want to get to the end game as quickly as possible so you can enjoy the rest of it without having to worry about the starport blowing up.

Now after saying all this I could be wrong cause I haven't played it in so long but I'm pretty sure that this is the method for making endurium.

these are the coords of the starport in sf2. so,

The fuel in sf2 is shyneum. It can be bought in alien races' cities. If you enter starport with endurium in the hold, it will cause a shitstorm.

If you still really want endurium, the best source is the mad Leghk in the past. They have battle jumpers, homing missiles, way heavier shielding than spemin, and they travel in huge fleets, but on the bright side, they do have a lot of endurium. i think there are ancients in 216, 45

The only usefulness of endurium in SF 2 is to sell it to the G'nunk at their homeplanet. If this is, what you want to do, just talk to them about trade when you encounter them in space. Perhaps they have some info, where you can find some.
You always find some at ancient ruins (the pyramids)
you can find them in ship wracks in the past (every race there uses endurium, even the dweenlee.)
But you shouldn't get caught, having endurium in your cargo by all but the G'nunk... I think even other spacetraveling races will react bad. (like the humna-humna.) And don't dare to bring it to starport. You will get a warning 2 days after the game starts in Operations.
If you want to know why endurium is banned in SF 2, I would recommend just to play the first part.