Western gun parts in Edmonton sells timney sears.
I've bought the volquartsen sear from brownells.
I've bought wolf springs from wolf directly.
In my opinion the volquartsen is better than the timney sear and it's cheaper. It is 99% of the time a drop in unit, while the timney needs you fit it via filing a hump on the backside of the trigger until your safety works.
Some guys go all out and buy a trigger and sear unit like that offered from rifle basix. They are the most money, but will give the very best adjustability.