A growing number of thrift stores in Canada are struggling to keep up with donations, as clothing piles up faster than they can sell, reuse, or give away. Oversaturation is leaving many stores with no choice but to send unsold items to the dump — an expensive and troubling outcome. The scoop Hand in Hand — a non-profit thrift store in Halifax — is dealing with daily overflow. "It's a treadmill. It doesn't end, it keeps coming and going," exec…