LTC1485 component in LTspice
There does not appear to be a SPICE model available from Linear, nor an model of an equivalent part (*75176) from other vendors. This is not unusual, bus transceivers are typically modelled in an IBIS environment (focusing on digital behaviour) rather than SPICE.

However, because there are IBIS models available from both ADI and TI for their equivalent part, as Andy pointed out, you have a couple options:


use an IBIS simulation environment, like Hyperlynx.
use a SPICE simulation environment which supports using IBIS models directly, like Microcap.
use a third-party tool (search "ibis to spice converter" in your search engine of choice) to transform the IBIS model into a SPICE model (this is often finicky, dependent on version, and can lead to poor modelling).


In this case, you may want to rethink your need for a SPICE simulation of this particular part.

Finally, if all you care about is the effect of the transceiver input on the rest of your circuit, you can also try and approximate the equivalent circuit of the input pins (ignoring the actual transceiver behaviour and output). Typically, an input pin is most easily modelled as a parallel R and C (in this case, R is stated in the datasheet, and C can be approximated from the package, but should be negligible at the speeds involved).

Also remember that simulation only takes you so far. If you require such a high degree of detail that you must have models of absolutely everything in the circuit, you may be looking at/for minutiae that may or may not be artifacts of the simulation. That's when the simulation cannot help anymore and a prototype is needed.