I'm not sure what is the "frontier" of theoretical computer science, but some companies, such as IBM Research or Microsoft Research, also make money by applying to some public funded research project, and as such, can work on rather theoretical work. For instance, I was involved in a project with some guys from IBM TJ Watson on security, and I can assure you that the work was rather abstract, and not at all IBM product oriented.
As for sites where such opportunities are listed, I'm not sure there are many, I'd say (but that's just my impression) that's it's usually by "networking" (i.e. you need to be involved with some guys from a company in some project, and then they might hire you). However, a good technique could be to apply for an internship first (if you're still doing your PhD), although it might a bit too late now, or even for a postdoc (if you've finished it). And in order to find the labs, I'd suggest to go to your favourite conferences, get the accepted papers, and scan for some big companies :)
EDIT: Concerning the sites where you can find job offers, I'd actually suggest to look for specialised sites in your topic of interest, where it can be possible to find offers from industry, rather than on larger sites. I guess most companies prefer to focus their search rather than dropping an ad on Monster, and receiving tons of irrelevant CVs.
For instance (although most ads will be from public academy, some are from industry, it can give you some pointers as to which companies can recruit, even if the ads are out of date):