Thurston,

You might have a look at the New England Custom Guns (NECG) site
http://www.newenglandcustomgun.com and see if they have a front bead that matches. Key of course is to be sure that your sight insert is the proper height to put rounds where you want them at about 100 yards. You might give them a call and also give J.J. Perodeau (named above) a call to see if he can do the job you need

Regards, Tim