So, I just recently got into glitchless speedrunning but I’m still very intrigued by all the glitches. How do you guys find them without some sort of program?

Ingenuity, creativity, a fairly deep knowledge of how the game works, and a helluva lot of willingness to try a bunch of things that won't work.

Along with the above method, you can also run the game through an emulator and use TAS tools to slow down the game for extra precision when it comes to trying different things. A lot of glitches can start as TAS only, and from there they can develop into something that’s RTA viable as people begin to experiment with setups and other parts of the glitch depending on what it is.

For a more naturalistic approach, there's many glitches that have been discovered by time, luck, and a willingness to research strange events. Communities that have been around for years can have players stumble into strange situations in their games, and when enough research and documentation follows up on these events, new glitches can arise.

you can try to mess around and if you manage to find a new glitch you can maybe use that glitch somewhere else to do more glitches