Unfortunately, the XP-100 was discontinued by Remington some years ago so there are no new ones available.
You might find one every now and then in a gun store. I've seen them at gun shows, but they're usually overpriced. They can be found on Gun Broker and similar sites. The last two I bought came from online from individuals w/ ads at handgun site classified ads. Stock XP's in factory chambers are going for $600-850 or so on Gun Broker and similar sites. $600 is used but not abused. $850 new in the box. Start adding some bells and whistles and the price could go up....aftermarket barrel, trigger, stock, etc adds value. Good scope base, rings, and scope can add value. I bought the aforementioned XP for $1100, but it came w/ a custom stock w/ some gunsmithing done to it, a nice Burris handgun scope, rings/base, custom reloading dies, one box of bullets and 20 pieces of brass. The most common chambers will include the 223 Rem, 7mm BR, 7-08 and 35 Remington. A good gunsmith can make one into whatever round a Model 700 can handle.
Some sites for classified ads: Specialty Pistols
My last two have come from here. Accurate Reloading Handgun Hunt Accurate Shooter
The same info applies to the rear grip XP.
Savage used to make a bolt action pistol, the Striker, but it was also discontinued. I've been very pleased w/ mine. Prices for a stock Striker start at about $450-500.
Of course, Thompson/Center still makes the Encore and Contender, both of which are fine handguns. Actually, I've killed most of my game using the Contender, not the XP.
Let me know if you have any other questions.