BNC Cables and their impedances
The characteristic impedance of coaxial cable is given by the equation
$$ Z =\frac{60 \Omega}{\sqrt{\varepsilon_r}} ln{\frac{D} {d}}$$
Setting
$$\varepsilon_r = 1$$
and
$$ Z = 10000\Omega$$
we get D/d = 2.4e72.
So if we set the diameter of the central conductor to 1 mm we get an outer diameter far beyond the diameter of the known universe. I think that such a coaxial cable is not available in your lab.
You also should keep in mind that your instructor is intentionally misleading you by introducing the resistor R1 with the same resistance as characteristic resistance of the coaxial cable he is writing about.
The intrinsic resistance of your source is given by your ideal voltagesource (when neglecting the diode) and is therefore zero. It is not 10 kOhm.