In terms of what's there now, I don't think you'd feel there was a lack of borrow even if they aren't as Dr Mac described them from when he first played them. However if you also play Mach Dunes their greens are probably closer to what Dr Mac was talking about.
I have not seen Machrihanish Dunes, because I didn't want to be accused of attacking the architect if I didn't like it. But my understanding is that the only part of the course that ISN'T natural are the greens, which were the 5 acres that were re-shaped.
My guess is that Machrihanish's original greens that MacKenzie loved were almost entirely natural. The only greens I have seen like that are at Askernish, and those have a lot more wrinkles in them than just about anything I've ever seen -- to the point that Mike Keiser wanted to pay us to soften them. [They made a bit more sense at 6 or 7 on the Stimpmeter than they would at 10, but when you've got a four-footer that breaks a foot even at slow green speeds, that's pretty difficult.]
I look at a green like the 2nd at Machrihanish and imagine there were a lot more like it to start with. But I don't know if any club history is really going to tell you that? They did share some photos with me that the bunkering was a lot more in your face to begin with . . . that hollow in front of the 12th green, for instance, was once a deep bunker.