Nigel,

Blaenwern, Hyfrydol, Llanfair and Aberystwyth (Parry) I am quite familiar with, the others on your list not, though I find
Calon Lan, Rachie, Trewen, and Llan Llynfi (apparently not to be confused with Llanfyllni!) in The CyberHymnal, and Blaencefn in the Christian Classics Ethereal Hymnary. So Gweddi Gwladgarol (which I take to mean "Patriot's Prayer") is the only one you mention that I can't find by Google, and which I would therefore much appreciate your posting where I and all can see and hear.

A few others I certainly think of as fitting your definition would be Cwm Rhondda, Rhuddlan, Llef, (and pretty much any other tune name starting with Ll or Rh, or having a "w" masquerading as a vowel), Bryn Calfaria, Gwalchmai, St. Denio, Ar hyd y nos, Nos galan, and Rhyfelgyrch gwŷr Harlech...

Haruo