The LTC1065 is 5th order Bessel lowpass filter in switched-capacitor technology. You are asking if it is possible to create a SPICE model by yourself - and my answer is: In principle - yes
However, I would not recommend even to start such a project. Surely, it is a lot of work and it requires a deep knowledge of filter theory as well as switched-capacitor techniques. Use your time for other interesting tasks.
I think, it is also important if you are interested in a model which can be used in the time domain (TRAN analysis) and/or in the frequency domain (ac analysis). In the latter case, it seems to be a bit easier to model the filter. In this case, you need no switches but time-continuous equivalent circuits which are available.
More than that, are you interested in particular in the LTC chip or - in general - in a 5th order filter?