Get used to building damage quickly with Falco. You'll do a lot better when you stop the mindset of: "Okay, they're now above 100%. I HAVE to get the stock." Just keep playing as you normally do, and keep building damage. Eventually they'll get to the point where pretty much anything you hit them with will kill them.
Learn your weakness. If you struggle to stock an opponent, then don't focus around something you can't do. If you focus the game around the one thing you can't accomplish, then you won't do so well. The best Falco's rarely go into "Need to get KO now" mode. They just keep spammin' lasers and camping regardless of their opponent's damage. They punish mistakes and wait for opportunities to throw an U-Smash or a B-Air. They rarely force a stock, but instead let their opponent fall into a stockable situation.
The main thing to understand is you WON'T consistently kill at insanely low percents. That's something Ike relies on to compete. Falco requires a completely different playstyle. He relies on quick, weak attacks to build damage quickly. In a match against Snake, you'll likely combo your way to 150% damage by the time Snake gets you to 80% damage.
Combo, string lasers, phantasm and always punish ending lag. If they get above 150%...then they get above 150%. They're THAT much easier to stock. It's not a bad thing that Falco lacks early kill moves as long as you can KO your opponent before he can KO you. That's the name of the game: getting the first three stocks and winning.
Over time, you'll find "getting the KO" becomes easier. Opponents make mistakes, and your U-Smash kills relatively early (around 120% depending on the weight). You have a spike, and other tools at your disposal.
EDIT: Basically, Falco doesn't have any reliable way to stock an opponent in the range you're looking for. But don't consider that a weakness. You're trying to use Ike's strategy of "hit hard and kill quickly before you lose" on a character who is quite the opposite.
