Early Rolling Block Rear Sight?

[Fox]

Any insight as to a rear sight for a pre-Navy contract Springfield Rolling Block in 50-70?

I was told that these guns used the 1861/1863 sight base with screw but there was a rolling block ladder.

There is a place in New York state that has them listed but said they are out of stock and he has no idea if they will get more.

Thoughts?

Thanks