This year I have heard just a few of them, a situation not helped by the fact that the two Thursday feasts have been moved to the following Sunday. Frankly, I find it depressing and feel a bit short-changed. I suspect there are quite a few people around who take the same view.
This has nothing much to do with the old or new forms of the Mass itself, but when it is celebrated in the vernacular, that is usually the end of the chant, and if the Mass is a sung one there are dreary Protestant hymns instead.
There is no excuse for this. There are about four different Ordinaries that have to be learned, the Credo and Pater Noster are, or can be, always the same, and the same is true for the responses. The sequences are not too difficult either.
The Propers, which are different for each of the Sundays and feast days, are another matter. They form part of the readings and people should have sheets or books with translations in their own language. This is actually an advantage, since most churches have rotten sound systems and congregations often come from many different countries.
The difficulty with singing these chants is not the Gregorian notation, with neumes. They are easier to read than five-line notation with round notes. But if, like me, you can't sight-read and can't find a recording, then there is a problem. Some of the Propers, and especially the Graduals are tricky anyway. Tones 3 and 4 are always difficult - that is a widespread experience in all the choirs I have been in. I have sung solo at when the regular cantor was away. I was note perfect on the train on the way there (don't worry, the carriage was empty), and then made a complete mess of some parts of the Proper. Which is why it needs more people if possible so that the music is not dependent on a soloist.
The Proper for the Precious Blood, for example does not seem to be recorded anywhere. There are quite a few others which have not been recorded. When this happens the Proper may have to be sung to psalm tones and they have to be written out.
Usually this site provides recordings and the scores, but the set is not complete.
There are some useful links from these sites
And notation here
Schola Gregoriana of Cambridge told me they are willing to arrange courses in Gregorian Chant outside the UK. They have good teachers available including one of the Solemnes monks. That is a good opportunity I think.
Liber Usualis is here, all 116 Megabytes of it.