Typically there's lots of places to get the C & N mount versions of this lens, however I have tracked down two options that you might like to check out, these are:
Camera Store:
Buy Sigma 30mm F1.4 EX DC Pentax Mount Cheap Online Australia | CameraStore.com.au They mention HSM in the text and you can see it in the photo, but the title only states 'EX DC'. This might be the older version (no HSM?), but an email could resolve that question. This is a widely spread bricks and mortar outlet, so not likely to be an issue finding a store. They are not likely to have much, if any Pentax, mount lenses on the shelf, but organising a pick up from a local outlet should be no dramas to arrange online.
Georges:
Sigma 30mm f1.4 EX DC HSM: Camera Lenses |Digital SLR Camera Lenses | SLR Lenses ? Georges Camera Shop Sydney I can't tell you anything about them, but a local Sydney person here probably could. This seems a really good price and they appear to have it in stock too, however doing a check by lens mount it doesn't appear under 'Pentax'. Again an email to the store could sort out whether they have/can get what you seek.
Anyhoo, hope this helps. Good luck
Tas