Please tell me like the AoM dungeon vendor who sells random level 75 blueprints that there is some vendor in the game who sells level 84 blueprints.
Farming Nemesis and leeching gladiator crucible games have net about 937372849 polished emeralds and 1 blueprint. Moments like this is where I tend to walk away from the game when grinding becomes a chore and Very Very Unrewarding.
To my knowledge there are no such merchants in the game. As an alternative you can try to craft random high level legendary items (except helms) using unique service from Bella Fald (AoM) or Algosia Fald (FG). You can find more details here.
Level 84 blueprints still drop at level 100. Yeah, it takes some time to get (almost) all blueprints. Crucible is one good source, another one is SR. Nemesis farming IMHo isn’t worth the time. If you can’t play high shards in Ultimate yet, you can also farm Normal or Elite in high SR shards. Something like level 60 or 70 in Normal will already give you a high chance of finding blueprints.
Keep in mind that you can only find blueprints you haven’t already learned. So the more blueprints you already have, the less likely it is to find another one.
Also make sure to check all the faction and other vendors. A lot of the “basic” and most needed blueprints can in fact be bought from vendors.
Have started to farm normal SR. Run Level 75/76 then get reward. Thus far have found any blueprints other than a ton of the Rune blueprints that must only drop in SR. (Think I have had 16 of those drop). As far as regular item blueprints I know I must be close to having found them all? I know I’m missing at least two but that’s when another blueprint drops that I never knew of and my shoulders drop and that grind continues.