So, as we all know, Time Rifts drop many Cosmetic weapons, which you can click and add to your collection. One example is the Valhalas Heartstriker.
I don’t know if this was always the case, but if you already collected the appearance of cosmetic item from Time Rifts, you can no longer buy the item from the vendor who sells it. Why would you want to buy it if you already have the appearance? Warlocks have Glyph of Felguard, which lets you Felguard or Wrathguard equip a random two-handed sword, axe, mace,or polearm from your bags.
This glyph DOES work with the cosmetic Time Rift weapons. I believe that the weapons should still be purchasable from the vendors, even if you already know their appearances. This benefits Demonology Warlocks who use this glyph.