There are some solemn tones, though not all that are in the Ordo Cantus Missae. For instance, it seems only the simple tone of the preface dialogue is there. On the other hand, the default greeting is solemn, while the simple appears in the appendix, and this is true of a few other things too.

Solemn Greeting tone(default)
Simple Greeting tone (appendix)
Solemn Penitential Act tone (default)
Simple Penitential Act tone (appendix)
Blessing - Solemn tone (default)
Blessing - simple tone (appendix)
The "Blessing - Solemn tone" is not to be confused with the "Solemn blessing tone"! Both simple and solemn tones for the Solemn Blessing are found here in the appendix.
Roman Canon (simple)
Roman Canon (Solemn)
Simple and Solemn tones for priest's prayers

This is just from a cursory perusal of the music on ICEL's site, not a complete analysis, so if I'm missing something or getting anything wrong, someone please correct it!

Jon

I guess I am missing a solemn version of the preface dialogue. Sorry for the confusion.