Trivia: Alan Ritchson, who portrays Rafael in this film and the sequel "Out of the Shadows," has stated that the actors portraying the four turtles were mistreated on-set and by the studio. As they were technically portraying animated characters through motion capture, their contracts were reportedly "full of loopholes" that didn't afford them equal treatment with the rest of the live-action cast, despite them being on-set full-time doing grueling work in motion-capture suits. One particular instant included the four turtle actors being kicked off set at the end of a 14-hour day without transportation home, while the rest of the cast and crew were given rides. They also weren't paid overtime like the rest of the crew, were barred from giving interviews despite portraying the titular characters, weren't invited to the premier, and were subsequently denied back-end profit shares from the sequel that they had been promised.
Trivia: When Splinter reveals that he knows April and she speaks his name, the camera pans over Mikey as he asks if she is a Jedi and he can be seen holding a can of Orange Crush. As promotion for the movie, Mikey was featured on the boxes of Orange Crush soda once the movie came out. Similarly with Donnie on Grape Crush and Raph on Strawberry Crush.
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.