This site has both the Gregorian, Fr. Weber, and LCM propers. Click the Sunday you want and then you can scroll down to view/download the Gregorian and English propers (as well as a psalm and Gospel acclamation) for each week. This week's listing is a week behind, but it's normally pretty good.
This page from the Corpus Christi Watershed archives has all the proper chants - full Gregorian and SEP - for Year A. Most also have practice vidoes, accompaniments, etc., though a few are missing here and there. Click the links for Years B, C, and feasts.
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