So in one game of 1.5.9 I was able to find a good amount early in the game (amassed about 20) but then did not hardly find more after that (about 30+ days in). In a second game I did not find very many early (just 5 or so) and continued to only find a few in the villages or towns rom time to time as the game goes on. So there's probably a little randomness as to how many get made and brought to town initially, then it probably get reduced by inventible imperials wars and may improve or not. I wonder if imperials are doing well do they buy more of them? This could explain the scarcity as when doing poorly= more raided horse villages or caravans, when doing well more rich lords buying them up. I know they don't use them for upgrades but I believe they still buy them.