well some where there is a broken or open pipe letting the sewer gas into your house. A vent pipe that is cut and capped might do this if its not properly capped right. you said you had your kitchen drain and sink replaced and re piped, well did they cut off the old vent and leave it in the wall so that sewer gas can come out? the only way you can get a sewer gas is to have a broken or open pipe. Go in the attic and make sure the vent bar is all in good shape and make sure no fittings and pipe came undone. In the attic the vent pipe goes out the roof and vents to the out side , if this pipe is cracked broken or came apart then you will get gas smell all over the house. the only way to find it is to use a gas detector and track down where its the strongest and then find and fix problem. Why did you have your plumber add air admittance valves? was there no properer vents on any of the plumbing? If you don't have the properer venting on your water fixtures then the pipe will siphon dry and the sewer gas will then come into your home. Vents , help the trap from drying out and also help take the sewer gas and put it to the out side.
I know this is not the easiest thing to find, but as a licensed plumber and the right tools the plumber should of found the source of the problem and been able to fix it right, let alone 3 different plumbers.....who are you finding , any licensed plumber with a brain would know how to deal with this and find the problem.
I have a gas detector and a camera i can put in the walls and look around and with my experience would be able to find the source of the problem.