Most IGA's are open. If u can find one of the bigger ones (ie: supa IGA or progressive IGA) you won't pay too much more than usual. I shop at the new 'Sista's IGA' every fortnight in Joondalup, as its cheaper than coles and woolies every time.

there is also a large one at Kinross, but its a bit of a hike for you, and im not 100% its open sundays.