Useful Links

All tagged art on Pixiv - http://www.pixiv.net/search.php?s_mode=s_tag&word=中野梓%20OR%20あずにゃん%20OR%20唯梓
(Tags: 中野梓 (Nakano Azusa), あずにゃん (Azunyan), 唯梓 (YuiAzu))

Waifu2x (zoom in and enhance qt Azucattes) - http://waifu2x.udp.jp/

http://iqdb.org/ and https://saucenao.com/ can be used to find the sources/full versions of images (click the ▶ on the post with the image you want to search).
If you see a screenshot posted and want to know which episode it is from, https://trace.moe/ will tell you.

The tag on most imageboards/Boorus (Gelbooru, Danbooru, Yande.re etc) is "nakano_azusa"

Image folders (click "Download as ZIP" in the top right to save):
High definition lossless Azusa K-ON Screenshots (1,338 images, 4.13GB) - [Unavailable for now]
2015 birthday art uploaded to Pixiv and Twitter (166 images, 121MB) - [Unavailable for now]
2016 birthday art uploaded to Pixiv and Twitter (348 images, 167MB) - [Unavailable for now]
2017 birthday art uploaded to Pixiv and Twitter (317 images, 143MB) - [Unavailable for now]
2018 birthday art uploaded to Pixiv and Twitter (--- images, ---MB) - [Unavailable for now]

/c/ Discord server:
https://discord.gg/vWd62pq

My Twitter (I try to retweet every piece of Azusa art that is posted, along with other official announcements etc):
https://twitter.com/KatarupaTwt