Welcome back! Curious to see how your random level generator thing goes (as you mentioned in another topic). Do you know that, for better or worse, there are now commercially published Lemmings games whose levels are actually procedurally generated?
Back on topic here, can you clarify whether you mean "All New World of Lemmings" (aka Lemmings Chronicles), or 3D Lemmings? The former only has Classic, Shadow and Egyptian tribes, there's no "space lemmings" or really anything space-themed. I haven't played 3D Lemmings myself, but I vaguely recall mentions of space stuff by others.
Or do you mean Lemmings 2: The Tribes, which does have a space tribe as one of the 12 tribes?
I believe all 3 games mentioned above now all have a functioning level editor written, which implies someone worked out how to extract the graphics, but I'm not sure how documented the details are, whether any tools actually exist to do the extraction (versus the level editor doing it internally for its own purpose), or whether the people who wrote the editors (or perhaps just the source code) are still around. 3D Lemmings at least is a recent enough development by namida that if you want its graphics, he can definitely help. I also seem to recall hearing people having made NeoLemmix styles out of (some of?) the graphics for all 3 games mentioned above. Maybe you can just directly borrow the graphics from those styles?