Howdy!
The xp-100 was introduced back in 1963 in the caliber you have. It was offered in Standard, Shilhouette, Custom and Hunter variations over the years and in .221 Rem Fireball, .223, .250 Savage, 6 BR, 7 BR, 7-08 and a few others. I believe they were dropped from the product line in the late '80s, tho I'm not sure on that.
From what I read in the gun mags, it appears that xp-101's never die, they just get recustomized into new configurations. :-)
Parts? Try e-gunparts.com; they might have what you need. Anyone else?
Good luck.
Michbob.