Thank you for your inquiry.
Firstly, I believe you have a Crystal Oscillator here, not a Ceramic Resonator.
Manufacturers rarely provide the C1/C2 values because the amount of stray capacitance designed into the circuit board needs to be spit into the equation.
I wrote on the subject of Load Cap Selection on a TechForum post here
Based on the above TechForum post the formula I have:
Load Cap value = 8pF
( 2 x Load Capacitance of Crystal ) - Stray Capacitance
(2 x 8pF) - 5pF < - Assumed Stray Capacitance
16pf - 5pF = 11pF
If you want to be super safe, plug into the circuit of the crystal every cap value close to 11pF and document when the part fails, and then use a capacitance value directly in the middle of the low and high values of failure.
I’m basing my equation on Atmel’s (now Microchip) AVR042 Application Note