You can get the Russian letter sha as follows:

1.  Make a file called cyrillic.sty and put the following into it:

\input cyracc.def
\DeclareFontFamily{U}{russian}{}
\DeclareFontShape{U}{russian}{m}{n}
	{ <5><6> wncyr5
	<7><8><9> wncyr7
	<10><10.95><12><14.4><17.28><20.74><24.88> wncyr10 }{}
\DeclareSymbolFont{Russian}{U}{russian}{m}{n}
\DeclareSymbolFontAlphabet{\mathcyr}{Russian}
\makeatletter
\let\@math@cyr\mathcyr
\renewcommand{\mathcyr}[1]{\@math@cyr{\cyracc #1}}
\makeatother
\newcommand{\sha}{\mathcyr{SH}}
\newcommand{\textcyr}[1]{%
   {\fontencoding{U}\fontfamily{russian}\selectfont#1}}

2.  Put a line 

\usepackage{cyrillic}

near the very top of your latex file, before the 
\begin{document}.

3.  Now you can use \sha to get the symbol.