Those analog switches come from the Land Before
Time To Make PSpice Models (vintage '70s / '80s).
However they also have (or had) multiple sources
and newer entrants might offer better support than
"legacy, milk it" incumbents.
A "family member" might be easily bent to suit, or
even something hardly-similar like a CD4066 (?)
analog switch. If you can get a running on, off,
leakage, resistance simulation you can fiddle the
model params. Or just build an analog behavioral
model of Rs, Cs, W (or whatever your available switch
uses for element prefix) or poly vccs and get the
care-abouts fitted "close enough".
Proteus specifically, I got nuthin'. Just look for alt
parts that maybe have direct, or "some assembly
required" CAD support. Check Renesas, whoever
Siliconix end up with, ADI et al for 40V analog switches.