Not sure there's anything you can readily replace the stock front sight with. Though if you are handy you could cut it down and modify it to take a match style front sight.
There is of course a Diana diopter (as seen on the 66, 75, etc) that would fit perfectly.
Or the Williams sporting peep sight - though I strongly recommend the older ones with click adjustments. The current ones are a bit crude.
The Chinese/Gamo diopters you can find for twenty quid aren't very good, and I would not trust them on any kind of springer.