Continuity mistake: When Leonardo, April, and Vern are hanging from the cliff after the semi truck falls off. April's arm is dangling beside her. The next shot from above, she is hanging on to Leonardo and then her arm drops beside her to dangle. (01:15:10)
Continuity mistake: Halfway through the film, when the turtles ask April to meet them on the rooftop, she is wearing a plain black top under her yellow jacket. In the next scene when the turtles have taken her to their lair, she is now wearing a light grey shirt with a symbol on it.
Continuity mistake: In the scene where the turtles are in the elevator singing MC Mikey, visible to the right of shot is the elevator's control panel and a light lights up every time they pass each floor. Just as the shot ends, the light lights up for floor 34. In the next shot, the elevator stops at floor 54.
Continuity mistake: There is a scar/cut above Raph's top lip. Through out the movie, it is constantly switching sides of his mouth.
Continuity mistake: In the scene where Raphael, April and Vernon are breaking into Eric Sacks' mansion with the Channel 6 van, the guards begin firing at the van and in one shot the windscreen is fired at and it shatters. A few seconds later, the windscreen is suddenly intact and the damage is reduced to just a few bullet holes.
Continuity mistake: When April goes to the rooftop for the first time, the ladder is a normal ladder that abruptly ends. When it cuts to her taking the photo, it is a ladder that curves over and connects to the roof, then when she is brought away from it, it briefly goes back to a typical ladder.
Continuity mistake: As the semi stops on the mountain, the camera pulls back to show the down slope, and it has trees and rocks all over. But after the truck starts sliding down and turns around, it now has a clear path to slide through.
Continuity mistake: As April increases the injection of adrenaline, the counter goes fro zero to maximum twice between shots.
Continuity mistake: When the turtles return April to the roof after erasing the pictures off her phone, she takes more pictures holding her phone horizontally. Then, at Eric Sachs manor when she shows him the pictures, they are shown to have been taken in vertical mode.
Continuity mistake: After the turtles, April and Vernon escape from the Sacks compound in the 18 wheeler, the truck then get stuck in the snow. When they realize they start to slide backward down the hill, Vernon guns it. But then they show the wheels spinning on the Freightliner Argosy Cabover with a single axle. Next shot goes to inside the cab and then back to outside the truck, and it's back to a dual axle truck.
Answer: While never really adressed, the most popular fan theories suggest that either: 1. Splinter manufactured the weapons with materials he found in the sewers or 2. Splinter scavenged for the weapons at a local dump or 3. They were ordered online (only applies to the 2014 version). Fans admit these explanations are kind of a stretch but certain scenes across movies and/or series lend credibility to one explanation or the other. 1. They seem to know how to improve or even craft their weapons meaning that someone taught them (Splinter). 2. They seem to be troubled when a weapon goes missing or breaks meaning they have limited access to spares. 3. Money doesn't seem to be an issue considering all the pizza that is consumed (in some cases the Turtles have been seen holding down jobs like tech support or birthday party mascot). The original purchase could've been made with money scavanged in the sewers and delivered to a P.O. box Source: https://tinyurl.com/y6kbxhlq.