Once upon old good times when chan sankakucomplex com was available for batch grab several rips were created
Sankaku 2014-2015 for interval 12.2013 - 09.2015
and Sankaku 2016 until 10.2016
with unique SFW content not found on popular that time imageboards
safebooru
e-shuushuu
and yande-re
.
Here is one more ancient jevel (created 22.12.2013) from the very start of imageboards era :
sankaku wallpapers set for even older interval 04.2013 - 11.2013 (ID 2380000…3480000)
with 27458 JPG-fied and deduplicated landscape images with rating:safe width:>=1920
File name contains one (first) copyright tag. Image size almost always original and rather big.
.
To be honest

• old Zerochan didn`t exists then and may partially overlap this rip
• a great share of images are landscape covers and other such stuff not intended to be wallpaper