Hi Sus,
You will need to get a referral from your GP to get the scan and ask him or her if they can recommend someone better this time.
I went to SKG at SJOG Murdoch with my first and took in a video tape so I could record it, which they were more than happy to do. The staff were really nice and patient and seemed as excited as I was even though they do hundreds every week.
I am now 17 weeks too and had my 1st trimester screen at 13 weeks at SKG Wembley, good thing was I didn't have to wait long with a full bladder, radiologist was nice enough but not very talkative. I am now booked in at SKG Mercy, which is where I will deliver, for my 19 week scan. I booked with Mercy because they do Saturday appointments which means DH can come.
Good luck, hope you have a better experience this time.