the maps are only expensive because of the leads, and due to the fact you cant really farm the maps and RNG nonsense
but like it was mentioned, they have leads all over the game
theres leads in trials, pvp, dungeons, overland, BGs, etc
if you want the lead, you partake in the activity which drops it
i dont enjoy the BG scene much lately because of how bad the queue times are when queueing in a 2 person group, but i still did them when they had the first round of antiquities to get the lead that specifically came from those
i have my main house (grand topal hideaway) listed in the housing tours, it has multiple target dummies, scribing altar, and grandmaster stations (in progress being filled out), as well as almost every antiquity furnishing on display to preview them