LaTeX:
\documentclass{article}
\DeclareFontShape{OT1}{cmtt}{bx}{n}{
<5><6><7><8><9><10><10.95><12><14.4><17.28><20.74><24.88>cmttb10}{}
\begin{document}
\texttt{Normal and \textbf{bold Typewriter.}}
\end{document}
ConTeXt: Put this in /usr/share/texmf/tex/context/third/type-loc.tex:
\starttypescript [mono] [computer-modern] [size] \definebodyfont [12pt] [tt] [bf=cmbtt10 at 12pt] \definebodyfont [11pt] [tt] [bf=cmbtt10 at 11pt] \definebodyfont [10pt] [tt] [bf=cmbtt10] \definebodyfont [9pt] [tt] [bf=cmbtt9] \definebodyfont [8pt] [tt] [bf=cmbtt8] \stoptypescript
and then:
\starttext
{\tt Normal and \bf bold Typewriter.}
\stoptext