If you're looking to get diagnosed for a particular thing before you go in you will bias the results of whatever screenings you get and the diagnosis will be meaningless. Take care not to say to yourself, "I want to be diagnosed with aspergers", but try to say to yourself, "I want to know what's different about my brain and why". I believe I have autistic traits but I have to be sure to give only objective information about my life, my specific feelings, and specific incidents or I know I will compromise whatever help I'm getting and waste everyone's time.
Start by visiting your family doctor (or community doctor/nurse) and telling him/her that you're interested in a referral to a psychiatrist. Your doctor will ask why, and you will honestly provide the details about your feelings that let you know or believe that there is something amiss with your mind. Your doctor will determine the best course of action be it referral to a psychiatrist or to other outpatient care.
It is very important to go in objectively and aware that just because Asperger's seems familiar to you, you may in fact fall into another category. If you leave out any experiences that don't support this diagnosis or otherwise skew the results to get it you essentially make your diagnosis meaningless and the help you look to receive may not be correct for your condition. If you're stressed by this, inform your doctor that you are worried that you may not be entirely objective.
I will end this by saying that while I know all the steps and parts involved it takes me months to work up to even the first step and I generally start to meltdown before I get far through the process and tell myself that I'm okay not knowing. I may be projecting my own pre-disposition but it sounds like you've made up your mind about what's wrong with you. If you aren't I'm sorry for all the unneeded information.