I have prepared a very quick and dodgy map of the homebrew shops I can think of in Perth.
The places, and a quick summary:
1) Greenwood - U-brew-it, with attached brewshop. Strictly K&K, hops on hangers, no grain, saf yeasts only. Not very knowledgable staff. Very little distilling accessories.
2) Osbourne Park - WestBrew, hops and good dried yeast selection in fridge, moderate grains, no liquid yeasts. Staff helpful. Some distilling gear.
3) Bayswater - International Homebrew Supplies. Owner is not a brewer, wholesale supplier to supermarkets. Hops in fridge, saf yeasts only, very little grain. Some distilling gear.
4) Midland - Cant remember. A few items tucked away in a corner of a cleaning supplies shop. Strictly K&K, hops on hangers, no grain, saf yeasts only. Not very knowledgable staff. Very little distilling gear.
5) Welshpool - Malthouse Homebrew. Good hops and liquid yeast (white labs). Decent grain selection. Staff variable (owner is good, helpers not quite so). Good amount of distilling gear.
Not shown on map - location is approx 20-25km due south of CBD, just off kwinana freeway in bibra lake
6) Bibra Lake - TWOC. Easily the best HBS in Perth. Excellent range, Roy (owner) is fantastic. If we could get another shop like this somewhere on the Northside, I would be a very happy camper. No idea about distilling, I didnt notice any when I was in there.
I hope this helps you mate

As you can see, there are large areas of the northside without a decent brewshop. I know that K&K would be your main business financially, but there's lots of opportunity to expand into grain and also distilling, which I hear is growing very quickly.
and everyone else...please feel free to add to this list, or correct me if you think I'm a tad off the mark.