there's an LA Times article that talks about who did the set design. Perhaps contact them directly?

http://latimesblogs.latimes.com/home_blog/2010/07/the-kids-are-all-rght.html

It looks pretty much like London Sofa from Mitchell Gold + Bob Williams. Have a look:
http://www.mgbwhome.com/LONDON-SOFABR-available-online--P10225.aspx
Good luck!

I'm nearly positive it's not Mitchell Gold but a sofa from HD Buttercup, a store in Los Angeles. It was a popular style for them a year or two before the film was released, so right on target for the set design. Check them out. Or go with the Mitchell Gold which will be similar (maybe not the same color) and probably a lot less expensive (though cheaper quality, certainly not a bad sofa!)

This looks similar to, although longer than my sofa, which is a Rowe Capri sofa. I bought mine in the now discontinued "pearl" color at Boston Interiors in 2004, but it looks more or less like this:

http://www.sofasgalore.com/sofas-and-couches/transitional-sofas/rowecaprisofalime.cfm

And yes, it is extremely comfy :).

Made also sell them, but are based in the UK
http://www.made.com/sofas-and-armchairs/3-seater-sofas/orson-3-seater-sofa-biscuit-beige

'Hot in Cleveland' has the same sofa: http://latimesblogs.latimes.com/home_blog/2011/01/hot-in-cleveland-betty-white-.html
Sofa.com has a similar sofa available in NYC: http://us.sofa.com/shop/sofas/snowdrop/