I have seen some people selling them on Dis/cord (you have to YouTube Search "MapleStory Cheat Engine" or "MapleStory Hacks" and scroll far cause they don't get much views). I cannot vouch that they are legit or scammers.
Only read the bottom if you want to make game hacks and know ASM lol:
If you have knowledge on how to reverse engineer/read ASM, you can try making hacks for private servers instead. Then, you can work your way up to GMS. I believe the hardest part about making cheats for GMS is the anti-cheat. However, some people have posted how to reverse the anti-cheat (and there are a lot of resources for it online). I am not knowledgeable on this topic, so I would recommend you do some research on this if you are interested in making cheats.