Is it acceptable practice to list solitary courses on an academic CV? I took some solitary graduate-level courses as a non-degree student at some US schools and plan to take further modules in England. These courses relate to my other degrees and certificates, but are from more elite institutions and provide more advanced, specialized training not easily found elsewhere. Is it acceptable practice to list solitary courses on an academic CV? What section and in what format might this appear in?
Acceptable?  Sure.  Useful?  Probably not.

If you're applying to graduate programs, then listing these courses would be appropriate.  On the other hand (at least for US schools), you need to submit official transcripts for those courses anyway.  Also, if you expect those courses to play a significant role in your admission, you need to make that case in your application statement.

If you're applying to an academic position that is primarily teaching, then listing the courses might be appropriate to show that you have at least taken courses on the topics you intend to teach.  But if you expect those courses to play a significant role in your hiring, you need to make that case in your application statements.

If you're applying to an academic position that is primarily research (including most postdocs and tenure-track faculty positions), there's no point in listing what courses you've taken.  With rare exceptions, your research record (as listed in your CV, described in your research statement, and judged in your letters) is essentially the only thing that matters for such positions.  Teaching experience might play a role, but classes that you've merely taken won't.  If you think specific courses significantly strengthen your case—making you one of those rare exceptions—you need to to make that case in your application statements.