Try a gemach. Or, alternatively, I am thinking about speaking to someone in my own community about this. Next year, I am probably going to move out of my mother’s house. The thing is that many of my clothes do not currently fit me but would be perfectly sized for teenagers. I had a hard time getting tznius clothes that would allow me to fit in with my friends without looking weird so I am thinking about trying to start a mini tznius gemach for teenagers who want to take on the mitzva but may be in a similar position (some of my skirts were like $50 when I got them).