Hack to get cross-platform fallback fonts with XeLaTeX.

font-fallback.tex

\suppressfontnotfounderror1
\def\myfont{Palatino} % Or whatever your primary font choice is.
\def\myfallback{Palatino Linotype} % Or whatever your fallback font is.
\count255=\interactionmode
\batchmode
\font\foo="\myfont"\space at 10pt
\ifx\foo\nullfont
  \font\foo = "\myfallback"\space at 10pt
  \ifx\foo\nullfont
    \errorstopmode
    \errmessage{no suitable font found}
  \else
    \let\myfont=\myfallback
  \fi
\fi
\interactionmode=\count255
\setmainfont[Ligatures=TeX]{\myfont}