What do you do when you want to simulate a signal (i.e with Hyperlynx) but you can't find the IBIS model of the receiver chip?
What parameters do you need? Where can you find them?
For a high impedance input, you can use a dummy probe (that's what Cadence calls it, can't remember the term for the Hyperlynx equivalent) which basically just looks at the voltages without affecting the signal.
Edit: In Hyperlynx you can find the models of probes, as the image shows.
A "real" IBIS input model will add some input capacitance, which you may also do as a separate ideal capacitor at the input. A few pF is common. Also a "real" IBIS input model will add pull-up/dn and pwr/gnd clamping diodes.
Since the pwr/gnd clamping tends to mask overshoot, I often use just an ideal input (dummy probe) and an estimated input capacitor for inputs when trying out different bus topologies and termination schemes.
Other than that, you may also be able to find the IBIS model for a 2nd source part (I guess you tried that already).