Love Philly? So do we. Let’s be friends. Sign up for the Billy Penn newsletter today. When Christina Kallas-Sartisogelou started Philly AIDS Thrift in 2005, she couldn’t have imagined what it would become. Her and a group of friends, who she says were self-proclaimed “lovers of junk” started small. “We just started bringing items from our apartments and begging our friends to do the same thing,” she said. “Gradually people started coming and d…