How did he score on the online Pervasive Developmental Disorder (PDD) questionnaire? Taking the printout from that to the psychiatrist could be a good start. it can also give you some ideas of the things to list, that are still an issue. When we live with kids like this it's hard to keep in mind what is normal and what isn't. We lose our frame of reference.
From our experience - you get a diagnosis wherever you can. You can confirm it later at your leisure because you will already have the ammunition you need to put extra services in place. For us - it can take ages to find someone prepared and qualified to make the assessment, and often it takes a series of different experts each working within their specialty. You may be able to track down a multidisciplinary facility which as always good for a diagnosis if you haven't already got one; if you have, it's good for double-checking it. But if you can get a diagnosis in the meantime from whoever is prepared to go out ono a limb then that's great. Much better than nothing.
Marg