Yondu tells Rocket he found them by adding a tracer device to Peters ship. However, Peters ship was built by the Nova Corp at the end of the first film after being destroyed. Disagree:The ship could have been unattended. There is no record of time between Yondu leaving and Quill being shown the ship. Plus they say, "we salvaged as much of the ship as possible". The tracker may have always been there.