According to the below article, Coulomb actually knew how to create equal electric charges without requiring his law.
http://www.jfinternational.com/ph/coulomb-law.html"
Also, he used cgs unit (http://http://en.wikipedia.org/wiki/Gaussian_units" ) where k becomes 1.
Let me elaborate a bit. Let's suppose Coulomb assumed:
F= k q_1 q_2 (where r=1)
He could also decide the quantity q1 is 1c [coulomb] and k=1 as he created the unit of electricity. This way, if we know F, we know q2.
He would repeat this process using different charges in q2 while...
Or how did Coulomb measure quantity of electricity while doing his experiments that leads him to claim his famous Coulomb's law.
F=k\frac{q_1 q_2}{r^2}
You can measure F and r for sure. But how about q1 and q2 ?