Looks like there are lots of possibilities on Digikey. Go to their product index and select "Integrated Circuits -> PMIC - AC DC Converters, Offline Switchers". Narrow down the selection using the input voltage range and the output power rating, and by checking the "In Stock" box. Choosing power ratings from 30W to 60W and voltages of 350V and higher cuts your options down to 95 parts.
Then sort ascending on price for quantity=1. The very first one is similar to what you need.
http://www.digikey.com/product-detail/en/FSFM300N/FSFM300N-ND/2078266 Fairchild FSFM260/300N. It's designed to perform many of the functions needed in an off-line (mains-powered) power supply, in power supplies for LCD TVs and so on. It uses current mode flyback operation, which I've personally used a lot and found to work well. It's highly integrated and cheap. But it's not designed for variable output voltage, and can't cleanly be adapted to work as an LED dimmer. It also needs a transformer, which you would have to make by hand. This can be a black art and should be considered NSFN (Not Suitable for Newbies).
In any case, we're now getting into an area where I feel uncomfortable advising you further. This is because this is a mains-powered application and I don't want anyone to try to hold me responsible for anyone's death or injury because of a mistake you made. If you want that kind of assurance from me, you'll have to get me to your place so I can watch over your shoulder.
I seriously suggest you pay for an appointment to talk to an experienced local registered electrician, about as much as possible, including personal safety when working with mains equipment, safe design and construction for mains-connected equipment, specific characteristics of the design(s) you are considering, considerations relating to the wiring from the switch to the light socket (which would be carrying DC instead of AC), fire risks, insurance issues, isolation and insulation requirements, whether it's legal for an unqualified person to build his own light dimmer for installation into his house wall, and any and all related matters, including ones I didn't think of and mention specifically above.
With that said, if you want to continue, do that Digikey search, note down all the manufacturers, and go to each one's web site in turn and look for switching power supply components with suitable characteristics. The data sheets often have a general application circuit design with real-world figures so you can see whether they might be suitable or not, so you should be able to eliminate many of them for various reasons.
Unfortunately, most switching power supply devices are designed for fixed output supplies, and cannot necessarily be made fully adjustable from 0% to 100% output voltage. A search on dimmers might produce more useful results.
I would also find out as much as you can about the internal design of the LED lights you're using, and the technology trend in general, so you don't put a lot of effort into something that soon becomes obsolete because LED light bulb technology changes.
Good luck!
Kris