To go about investigating the rom-com audience I would consider:
- online searches, variations of 'rom-com box office' with other keywords such as 'uk' 'world' 'all-time' etc
- blogs and columns dedicated to box office analysis, not least the Film Guardian series on UK, US or global box office
- check the Wiki entry to see if there is a box office list/discussion
Images + video/audio clips were included in this audience research vid - look up book indexes and have a flick through magazines/journals such as Sight and Sound or the Media Magazine
- have a look at the archive (and links lists) on my BritishCinema, AS Coursework and Rom-Com blogs
I've had a quick look at some of these, and have picked out just a few points below. Be clear on why you are researching the nature of any genre's audience (or market):