Does anyone know of anywhere to buy a Blu-Ray demo disc that goes through the audio/video upgrades like Best Buy plays?

You can ask - they usually will throw them away when a new one arrives.

I tried that and they said they wouldn't, could try again though if they do get upgrades often.

You can find some on eBay

There's a very cheap ($6.99 or so) sampler DVD, plus one called Digital Video Essentials: HD Basics that is mostly for calibration. You might also want to check eBay as someone else suggested, not only for the Best Buy ones, but perhaps some of the "free rental" ones that were available from video stores when Blu-ray was introduced.

I emailed Dolby and DTS and both sent me a couple free demo BDs.