You can just craft and obliterate items and then use the Blizzard item restoration to get them back and reobliterate them again or you can of course restore some old items if you already have progression on it.
In theory if you have 0/50 on this achievement you just have to craft 25 items.
Important thing : you have to keep the Obliterum Ash to use the restoration or you will not be able to restore items.
Also you can't restore PvP gear that you obliterated.