Your best bet might be to do as Joe suggested and visit a gunsmith or gun shop. They may have something available that would work. The Pacific aperture sights are long out of production. The website below is from Lyman and lists some current offerings.
http://www.lymanproducts.com/lymanproducts/index.htm
It might be more helpful to check out Brownell's website or give them a call for assistance.
http://www.brownells.com/Default.aspx
All the best...
Gil