I moved your question about the AD8368 in the RF Components Community. Someone here should be able to assist you.
Unfortunately, there are no full or partial models for the AD8368 VGA. As the datasheet says, it is 50 Ohms input and output. I don't have the equivalent shunt C/series L that could model Figures 18 and 20. I'll see if I can get that data but it will probably be a couple of days.
Hope this helps,
Here is the S-param data.
Retrieving data ...