There is no aftermarket solution to this. They are however very simple to make if you have basic fabricating skills, it's just a rod from the bucket mounting shoe that slides though a tube mounted on the FEL frame. We can get you pictures if your interested...
But it shouldn't be to expensive at the dealer though.
I have one on my 410 loader and never look at it anymore, I just learned to watch the bucket. The top of the bucket is on the same plane as the bottom, so if the top is level-so is the bottom.