My suggestions are going to revolve around food tours and very Asian centric, so apologies in advance.

I follow both these people on Twitter so know of them. Robyn runs occasional food tours from Eating Asia. Here's her website - http://eatingasia.typepad.com/. The other gentleman from Mumbai that I know of is Finely Chopped's Kalyan. He gives an awesome insight into Bombay's food. You can find more about his walks here - http://www.finelychopped.net/p/finely-chopped-waks.html.

The other option but you will need to do a fair amount of location based searching is http://www.tourhq.com/. Its a relatively young website, guess, similar to Viator. I think you should be able to find food guides on there.