Ah okey, offlinemode is not necessarily what you want.
Aight to get this puzzle together.
Each baord has a config file to determ the board family: https://github.com/armbian/build/tree/master/config/boards
In your case sun8i.
Then there is a source config to determ which sources to be used on a specific board family: https://github.com/armbian/build/tree/master/config/sources/families
Still in your case sun8i. But you won't find any linked sources there.
There is an include in the config that inludes sunxi (which is general term für the whole family, to say sun4i, sun8i, sun9i and so on).
So check this include and there you will find the linked sources.
At this very moment there are three branches filled with these kernel versions:
- legacy: 4.19.x
- current: 5.4.x
- dev: 5.6.x
If none of those matches the kernel you are looking for you have to search in the file history for changes. Some I can remember is that last year the support for old-legacy 3.10.x and 3.14.x has been dropped. And current (which name was "next" back then) was on 4.14.x