Rich the jr gent II is a moving target. Originally, the Heritance nib was made to fit the Jr. Gent II, now they do not fit correctly in some versions of the pen. So, I surmise the pen is different than it was.
When I was doing shows, there was no one selling parts, as far as I know. So, to solve the problem you are facing, I would have found the least expensive pen of that type (chrome jr. II) and purchased the fountain pen, then swap parts. I sold pens with enough margin that I could afford to do this, as well as it giving me extra parts.
Now, I don't think that would work!!! Cause the jr gent II family is no longer universally interchangeable.
Good luck!!