According to Amazon.com, Tom Riley fans in the US and Canada can pre-order the Region 1 DVD for Ill Behaviour. Though you have a very long wait, as it seems it wont be released until October 9th 2018. If you are impatient, and have a multi-region DVD player, the DVD is available in Australia and UK.
Tom Riley stars as Charlie, alongside Chris Geere, Lizzy Caplan and Jessica Regan. Ill Behaviour, written by Sam Bain, was broadcast in the US on Showtime, and for those with a Showtime subscription, it is available to watch online.