I’m always on the lookout for good malware datasets so decided to keep this log of online repositories.
VirusTotal have an API and allow yout to refine your search based on a number of factors such as: number of AV scanners that have marked the sample as malicious or trusted; protocols (e.g. http); network activity etc
VirusShare have a bucketload of samples and have very kindly curated some useful sample sets (scroll to bottom of the Torrent page) for Android, Linux, 64-bit Win and Ransomware
Maltrieve is not something I have used but looks like an interesting crawler for Malware across a number of sites