On the ask of a member of the forum, I just ported CM 12.1 to the "a51ul" HTC Desire 820.
I cannot test it with my personal device, who had his release-keys modified because of Tomal's Discovery V2.0.
Waiting for your returns, and hope you enjoyed.
[ROM][CM 12.1], ROM for the HTC Desire 820
ROM OS Version: 5.1.x Lollipop
Based On: CyanogenMod
Current Beta Version: 1.0
Last Updated 2016-04-04