The most classic case of the Greek Gift in the French should never really happen because any French player ought to know this. It is in the Classical Variation. The move 9...cxd4 is a blunder and Black must play 9...f6 or 9...f5 (both are fine).
True I agree it's a bit hopeful to think French players will fall for it, but if you prevent them from castling hey that's something too right?
This example is a bit less straight forward... When Black goes up a pawn (Milner Barry has great stats check it out) and things get a bit complex they could potentially blunder more easily than in a "known theme" like you mentioned... Knowing tactics in a resulting middle game is helpful even if you don't get to play them.
Besides OP is not an advanced player like yourself 
I like this post it shows something quite instructive!
I never consider Greek Gift if there is a Bishop on e7 and a Queen on d8 cuz they defend the g5 square right? And to me Ng5+ is like my "OK" to safely Greek Gift if it can't be captured.
But this pattern is one to remember! If you can shoo the knight to go misplaced on the rim you can regain the piece like you did with Qxh5+. Nice.
Later, Ne4 is maybe a bit hard to spot but perhaps the thought process to find Ne4 targeting f6 is to understand that f6 is weak because if gxf6 that pinned bishop gets captured with check. Easier said than done. How do you realize f6 is weak? try to think how can I cash in on this, as of now, "only annoying" pin... Oh, bishy is defended by a lone g pawn maybe I can divert that pawn... how... f6 is weak... etc...
Cool pattern tho, and I wonder if there are other patterns where you can Greek Gift despite bishop on e7 and queen on d8...
Also... If you want to get the Greek Gift play the Samich Attack vs. Alekhine (it's kindof like a reversed Stafford, check it out. Alekhine players don't face it so often it's pretty solid and you get a middle game with Greek Gift ideas.) [1. e4 Nf6 2. e5 Nd5 3. Nc3?! Nxc3 4.dxc3 ]
Also in the Tarrasch/Advance French... or in many French you can aim for a middle game with Greek Gift ideas... There are probably more that I don't know. But always remember when you face the French.... You may very well get a stunning sac, it works, it's great, but these guys know how to wiggle out, they play the French. so don't celebrate just yet. You must continue to find ideas that will hurt them the most.
So if you want to get the Greek Gift more, you should know through what openings you reach middle games where it's a thing.
Knowing which opening it arises from will allow you to trick them into castling when they actually can't possibly.
Good luck thanks for the post
The most classic case of the Greek Gift in the French should never really happen because any French player ought to know this. It is in the Classical Variation. The move 9...cxd4 is a blunder and Black must play 9...f6 or 9...f5 (both are fine).