You must speak with the Ofieri Merchant located at the Upper Hill fast travel point in eastern Novigrad. Purchase the following items:
~ Decorated Saber - ~2500 crowns
~ Ofieri Blinders - 233 crowns
~ Ofieri Saddlebags - 233 crowns
Back out of his inventory menu and comment on his horse. This will start a conversation which leads to racing him. If you win the race, you will receive an Ofieri Saddle. Now speak with the Merchant again and exhaust all of the dialogue options until Geralt mentions that he can recover the Merchant’s lost diagram pages. This will start the “From Ofier’s Distant Shores” quest. You may do the quest however you want but three of the four diagrams are located at campsites that you will be looting for the Wild Rose Dethorned achievement. Once you have collected all four diagrams, return to the Merchant, meditate for 24 hours and then collect the diagrams for the other pieces. Once you have crafted the items, your set will be finished and the achievement should pop. Here is a video to aid you:
Full credit for the video goes to Guides Gamepressure.