I get that question often, with people wondering where I came across the very real-world-looking placards and stickers that I have on the dash, the throttle quadrant, and elsewhere. The answer is Screaming Aero Graphics, which sells interior and exterior placard sticker kits for a large variety of aircraft. I purchased mine on eBay, but they have since opened a full-service website where they sell all sorts of aviation decals (including striping, registration numbers, and more).
I purchased the Cessna 182 kit, and it was easy to use. Just peel and stick, and where a sticker didn’t quite fit my panel (like the flap detents on the throttle quadrant) I just trimmed it. Easy. Service was quick and correct and pricing was fair. Check them out.