Practical advice time, folks: how do I find interesting films showing in London cinemas?

I'm particularly interested in older and moderately obscure films -- the kind that will turn up over the course of a year, but that I'll miss unless I inhale a listings magazine every week.

Does there exist a website that can take a wish-list of films, and email me whenever one of them is on in London? That seems like such an obvious and potentially-profitable concept that somebody must already have built it, but I can't find it.

Relatedly, does anybody want to come see some films with me?