cmttfont is already pretty bold (by comparison with other fixed-width fonts), and bold small-caps is not popular with many professional typographers). There’s a set of “extra” Metafont files on CTAN that provide bold versions of both
cmcsc(the small caps font). With modern TeX distributions, one may bring these fonts into use simply by placing them in an appropriate place in the texmf tree (these are (La)TeX-specific files, so the “public” supplier would be an appropriate place). Once you’ve rebuilt the file indexes as necessary, TeX (and friends) will automatically build whatever font files they need when you first make reference to them. There’s a jiffy package bold-extra that builds the necessary font data structures so that you can use the fonts within LaTeX. Another alternative is to use the EC fonts, which come with bold variants of the small-caps fonts. If you need to use Type 1 fonts, you can’t proceed with Knuth-style fonts, since there are no Type 1 versions of the mf-extra set. There are, however, Type 1 distributions of the EC fonts, so you can switch to EC and use them; alternatives are discussed in 8-bit Type 1 fonts. Of course, commercial fixed-width fonts (even the default Courier) almost always come with a bold variant, so that’s not a problem. Furthermore PSNFSS will usually provide “faked” small caps fonts, and has no compunctions about providing them in a bold form. Courier is (as we all know, to our cost) freely available; a far more presentable monospace font is LuxiMono, which is also freely available (monospace text in the typeset version of this FAQ uses LuxiMono, with the metrics and LaTeX support available on the archive.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=bold-extras