WTB Boy's Cycling/Tri Apparel

Fellow BTrs. My 9yr old has signed up/committed to his first tri, without any pressure from me. He has been attending the intro clinics, and training with me (it's been very enjoyable to have him biking alongside me on my long runs, or sharing a lane on mellow swim days). He wants to look the part, but with how quickly kids grow and can change interests, I'm not going to dump a bunch of $ into this first one. Anyone hanging on to any gently used and outgrown jerseys/shorts, etc. that they'd like to get a few bucks for? He's 9 and in between a youth size small/medium. Thx!