Marbles make a good replacement sight if you want to stay with standard type sight, their standard flat top is what most use- doesn't fold flat like the Marlin sight but has a smaller notch for better accuracy. They also do fire sights which are good for low light conditions.
Brownells should be able to help you out.
I have a spare sight (might cost you a bundy or two) but not the adjuster ramp
it may be better to get a new sight than a second hand one so you can fit it to you guns dovetail as used may be undersized- new are oversize and you have to polish it down to fit.