This is really sound advice: if you want to get a feel for good Cornish, then make the effort to read good Cornish, especially historical Cornish. Use your course/grammar books to get you started, but move on the the texts as soon as you can.Read the texts, folks.
The historical texts are the bed-rock on which the whole Revival rests, the lode-stone that should guide our course, the touch-stone that lets us tell the gold from the dross. There are plenty of editions of these older works, some in the original manuscript orthography, some transliterated into various forms of Revived Cornish, and many of them with parallel English translations. Many of the older editions are available free for downloading from the Internet Archive.
One of the most comprehensive sources is the compilations "Looking at the Mermaid" (A Reader in Cornish Literature 900–1900), ed. Alan M. Kent & Tim Saunders, available from either Amazon or the Book Depository.
If you want a good overview of the history of the language, and the early Revival, I recommend 'The Cornish Language and its Literature', by Peter Berresford Ellis (out of print, but available 2nd hand from Amazon), along with his shorter 'Story of the Cornish Language'.
The literature in Revived Cornish contains some excellent writing (and some not so good, frankly). My all-time favourite is ASD Smith (Caradar), including his short stories and his verse epic 'Trystan hag Ysolt' (available from Spyrys a Gernow). Other writers who do very good verse/prose include Robert Morton Nance, Myghal Palmer and Nicholas Williams.
