If you're looking for a rear sight for your XP-100 for silhouette shooting, this one is surplus to me:

Made by Iron Sight Gun Works, will fit the front action ring of the Remington XP-100 and clone actions. Appears to be very well made, on par with the BoMar sights I have on my XP-100 7TCU.
Price is $30 shipped via USPS priority; payment by check or money order. Thanks.