Although not a specific "scrap booking" supply shop, Educational Art Supplies at 17 Hampden Rd in Nedlands is a treasure trove of "stuff". Two floors of everything from pipe cleaners to felt, glue, crayons, paints and stickers.
I did some lessons at a gorgeous little place called Tomorrow's Memories at Bassendean, on Old Perth Road. It's a real gem with lovely products, convenient kits, scrapbooking evenings, competitions and classes for adults and children. Their website is: http://www.tomorrowsmemories.com.au/index.html