Getting leads for Ancestral Motifs can take forever, because we don't have a way to obtain treasure maps for a given zone (there are some activities/containers that have a higher chance to contain maps but the map pool is huge!).

My suggestion is to add treasure maps for the zone you are in to the bonus loot from excavation. Thus you go to the zone where you are missing the motif/motif chapters and just start scrying and excavating and "farm" maps in order to try for leads (which aren't guaranteed) for your missing motif. (ie. Need Ancestral Breton leads, excavate in High Isle and have a chance to get maps from your extra excavation loot!)

I don't know if there are even enough maps looted on the server for everyone who wishes to unlock all the Codex entries to do so!

It would still be time consuming, require effort, but actually offer a chance for us to work towards it that isn't rng loot or buying up all the ones you see on stores.

Ancestral Akaviri is the only one I completed, Blackwood maps were quite common during the Bounties event, which was great for those of us who were playing then. Everyone who wasn't has the same issue as we do for the rest of the motif leads.

It is also rather unfair that these motifs (at least Ancestral Reach) are in the Master Writ pool!