I had a points-rebounds-blocks triple-double, but that was years and years and years ago.
I think the SIM is set up to minimize the chances of having a single player having many steals or blocks. It seems if you have a player get 3 or so in a half, the chances of getting more are very low.
Assists are lower than they should be as well, I think. You can have a PG with like 60+ in REB and he won't get enough rebounds in this game for a triple double. You also won't have any non PG get 10 assists regardless of their BH/PA ratings. Or if you do, it's a rarity.