You have my sympathy. Was in a similar situation and tried lots of things... hiding myself in a conference room, headphones, being artificially mean, blocking out parts of my calendar as alone time, telling people I preferred to be left alone for the next few hours - unfortunately none of it worked because when people want something from you their impulse is to turn around and ask you when the barrier is so low. I'll admit that it wasn't a one way street, I probably unknowingly did it to people when they were in the zone.

The only thing that really solves it is if you can convince your employer to let you work remotely even a day or 2 - thats when I actually got to do real work. Just my 2 cents.