What is the typical resistance of a piece of 1 cm^2 of carbon paper?
If there is no published resistance for that carbon sheet, then the best choice is to do exactly what you have done, i.e., measure the resistance per square. However, that specification is in given in the Strem catalog! It might be difficult o find if you do not spell the company's name correctly.
Two notes:

Resistance of a uniform, homogeneous sheet is measured per square, not per cm2. Whether the sheet is 1 mm on a side, or 100 km on a side, the resistance from one edge to the other would be the same; in your case, 3 Ω. [Consider that making the separation wider between edges is exactly compensated by the increased length of the conducting sheet.]
&quot;Carbon paper&quot; referred, in English, to paper with a mix of lampblack carbon and wax, though now it also applies carbon microfiber paper. For clarity, I suggest using the name Strem uses in it's catalog.