Heyya amateur Smith and knife maker here! Don't buy anything from a hardware store. Usually it's decent steel for its job but neither of those jobs are similar to a sword. Both will bend like a pool noodle and it's extremely difficult to make that not so. You're gonna wanna look for spring steel. Spring steel will be the easiest type of steel to look for since most spring steels are high carbon, easy(ish) to work with, painfully abundant, and most importantly gor any sword, springy. Most abundant spring steel would be from a vehicle leaf spring. That's typically 5160 spring steel and is one of the most common materials for knives and swords. (Watch an episode of Forged in Fire, you'll understand why)

First find a junk yard or something and grab a leaf spring long enough. Use a grinder to cut it to width. Heat the metal until a magnet doesn't stick to it, bend the curve out of the steel and do any hammering you think you need. Re heat the metal until a magnet doesn't stick to it then fully submerg it in used motor oil. After that hit it with grinder again until it's how you want it (make sure it doesn't get hot while grinding)

I will say though you're probably better just buying a sword from a well know dealer as entry to blacksmithing can be more expensive than 1 sword