i have two XR45 Barrels remaining. i have scoured the planet for more of these, but by my count, unless someone that picked up a spare from me decides to sell it, the well is dry.
XR45 Stainless Barrel standard length
less than 10 rounds through it. like new. $400.00
XR45 "Onyx" Barrel "Long" (apx 4.2").
with the difficulty involved with manufacturing this barrel, there will be no others coming on "aftermarket".