Where to buy legit signed memorabilia?

My daughter is a huge Max Christie fan and he was the main reason why she even got into basketball and became a Lakers fan. I’ve been trying to find Max Christie signed memorabilia to buy her for Christmas, but I’m afraid of counterfeits. Does anybody know of legit places to buy? I came across a place called golden state memorabilia, but in not sure how legit they are. Any suggestions?

PS- she would want something from when he was on the Lakers, not the Mavs.