Well, you can go to eBay to drop some cash on an actual Cowichan Sweater.
OR you could go to 80stees.com and get a knock off version.
But if you are especially crafty (or if Grandma wants to know what to knit you this year instead of those rainbow potholders or orange and avocado afghan), check out Andrea Rangel Knits, who so kindly offers a free pattern to recreate this thing of beauty.
Take note, she said it was HARD to recreate this! But it’s cool. The Dude abides.