The knitting is a ribbed knit stitch which is actually knitted right into the sweater when they make it. Knitting machines can do that. Well, so can knitters working with needles but sweaters like the one in the picture are machine-knit in bulk. Making it look like that without actually knitting ribbing....is not easy. Anything that involves making fake stitches or painting/drawing lines on a plain fabric will not look like ribbing, it'll look fake and painted.
When it comes to the plaids used in animation...if it's not an actual tartan (google tartans and Scotland, it's amazing) then chances are you won't find it just sort of existing out there unless you're really lucky. And even then, it might be in a fabric which isn't appropriate for what you need to make. If you need a special non-tartan plaid in an appropriate fabric for, say, a skirt or pants, you may be out of luck. Ways to make it yourself vary - I've done ribbon-stitching, and it isn't the method I would recommend. I might lean toward paint, but it would make fabric stiff. Unless you can find a means of getting it custom-printed or specialty-woven (expensive and hard to do!) then your options are limited.
Founder and President, Madison Area Costuming Society, a chapter of the International Costumer's Guild
Strange Land Costuming - www.strangelandcostumes.com