You can still find them here,
"We have recently bought out all of the Barnes MRX bullets in existence! Once they are gone, they are gone. They will be packaged in a Doubletap box in the quantity ordered for your convenience.
Super premium Maximum Range X Bullets feature a polymer tip, flatter trajectory and greater retained energy at long range. Patented Silvex core aids ballistic performance and accuracy while retaining virtually 100% of its original weight after expansion. Similar to the Triple-Shock X Bullet, the MRX features a tungsten-based core that makes them slightly shorter, which in turn increases case capacity.
I ordered 6 boxes of the Barnes 338 250 grain MRX and got them faster than I expected... in 6 days I think... and this is to Alaska, very fast, surprised the heck outta me !