well if you have a plush pikachu, you can just sew a little swatch of long-pile yellow fur onto it's forehead, probably.
is awesome, they have long pile fur and you can get a 3"x4" swatch by mail. If you join you get 10 free swatches and shipping is free on your first order, so if you're not already a member, you can get this little bit totally free. *grins*
I'd recommend this fur in yellow:
Or this is longer-pile but has sparkle to it. I'd get a swatch of both and see, heh.