We introduce the "Intonation" dataset of amateur vocal performances with a tendency for good intonation, collected from Smule, Inc. The dataset can be used for music information retrieval tasks such as autotuning, query by humming, and singing style analysis. It is available upon request on the Stanford CCRMA DAMP website. We describe a semi-supervised approach to selecting the audio recordings from a larger collection of performances based on intonation patterns. The approach can be applied in other situations where a researcher needs to extract a subset of data samples from a large database. A comparison of the "Intonation" dataset and the remaining collection of performances shows that the two have different intonation behavior distributions.