Where to get Skinny/Slim clothing in Sydney?

Try Chinatown, especially around Goulburn St, Sussex St and George streets.
You'll find "Asian size" clothing fits tighter, but be warned- some of those places are more suited to skaters and homeboys.

There's one place on Goulburn, opposite Baskin Robbins, which might have the slim stuff. It was quite pricy, I believe.

Also, Galleries Victoria, near the Hilton has one place in particular, I think it is called "incu," near the Brent Wilson and Nu+Nan shops. It is ridiculously expensive, though.

incu is rather expensive, with $200 tshirts and what not, but hey - if you want to be trendy thats the place to go. I tend to think that Chinatown's stuff is really bad quality, even the more 'high end' stuff. I'd still say go for Myer, and GP/glue and other stuff if you're not afraid of trying on clothes of the opposite sex.

Supre.