Where can I get a paper copy of a certificate for a certified system?

The short answer: from the vendor who makes the certified system.

The long-ish answer:

We get this question on occasion. In reality, it's not up to Canonical to provide hard-copy of certificates, but rather the vendor who makes the certified system.

When a vendor system is granted Certified or Certified (Pre-Install) status, that vendor is allowed, to a certain degree, to use Ubuntu logos and such to create marketing materials. This could be anything from a simple web page to actual hard-copy information sheets, paper certificates, advertisements, etc.

With regard specifically to paper certificates, however, in general, vendors prefer to simply point customers to the listings on the website rather than print out or distribute certificates. In cases where vendors DO wish to provide actual certificates, doing so is entirely up to the vendor.