What is the PSPICE model of my probe + oscilloscope?
It would look something like this:

A lot of this is assumed and depending on your requirements for accuracy, you will need to determine a lot of these values empirically for your probe.  The values, especially for the compensation network will be highly specific to a given probe's rated bandwidth.  Tip resistance can also be as high as 250Ω for lower bandwidth probes - regardless, it is definitely not zero.  The AC coupled noise is added mostly for academic purposes.  It will be so highly dependent on the environment, the probe's location and orientation within that environment, what lights are on, if someone is using an angle grinder within 100 feet, the angle of the tongue of an invisible cat that may or may not even exist, and all sorts of other things you can never hope to account for.  As long as your probing techniques are decent, it should minimize the influence of any of this noise so for myself, I would just omit it.  But it is shown for completeness' sake.
This is based entirely off of this excellent article in the October 2009 issue of Silicon Chip by Doug Ford which you can read here.  I've summarized his final conclusions in the form of a SPICE, along with pertinent comments.  In the article, transmission line parasitics of the cable are determined empirically and vary slightly depending on the bandwidth of the probe.  Other values, such as those of the compensation network are determined largely by trial and error, by stepping through values and seeing which results in the minimal peaking and other effects, which is what the designers of the probe were also attempting to do.
Ultimately, you're going to have to determine a lot of stuff about this probe by measurement or just some trial and error where you try to make the simulation look like a real waveform capture of the same thing, and possibly disassembling the probe so you can measure components directly.  Depending on how accurate or inaccurate you need the model to be, this can be either a fairly straight forward task with the understanding of a generous error margin being present, or a tedious and laborious task.  Good luck.