Unseen Menace and Knife of the Undermountain King both crit on 19, though the Knife actually applies that to all weapon attacks you make so it's effectively +1 crit range. Other weapons like Dead Shot or Bloodthirst can improve your crit range, and since they stack you can get +3 crit from your weapons, +1 from Champion, +1 from the Elixir, +1 from your helm, and a conditional +1 from your cloak, letting you crit on a 13+ if hidden. With advantage this is a 64% crit rate. That doesn't make it a good build of course, absolutely none of those things help with the damage you do when you crit so baseline the only benefit of all of that is an extra d4 or d8 damage 64% of the time meaning it's worse than Hunter's Mark. But if you want to crit fish, you can do it.
Sword of Life Stealing gives a return on getting crits, as do the Craterflesh gloves, and of course anything that gives bonus dice of damage in general. A good crit build can certainly be built by balancing crit enablers and payoffs of course, but yeah, all of that effort and it'll still be less reliable than just paralyzing them.
