Please help me, help my Kinderguardian!

I recently got my boyfriend into Destiny 2, and he's been enjoying it a lot so far. He's a hunter, around level 14, and we just finished Io. His favorite weapons in most games/media is bows, and so I'd love for him to be able to grab Orpheus Rigs from Xur this weekend. Problem is, at his low level, the number of reliable ways to get legendary shards seems low. Does anyone have any advice for a good way to grind out shards tonight and tomorrow for someone around level 15-20? I'm hoping to finish the campaign tonight with him, but then I'm not sure if strikes, crucible, public events, or something else is the next step.