So recently my fighter got access to a single spell as a part of becoming a gods herald of sorts. And i know i can make an item that allows me to cast spells with a certain amount of charges but i was wondering if it was possible to give my character a spell with the slots outside of making an item/copy of a subclass/feat?

Your options are:

1. You can make a magic item with a number of charges of your choosing.
2. You can make a feat with a number of uses of your choosing.
3. You can make a subclass with a number of uses of your choosing or the spellcasting feature which will give them the Eldritch Knight spell progression.
4. You can make a race with a number of uses of your choosing.

Making a feat or a magic item is the simplest way to do it.

I figured there wasn't any other way, which is a shame. I have made it an item.

Keep in mind that it doesn't need to literally be an item in the game. You can call it "Kord's Favor" or something, set the weight to 0 and you're good.

I'd use items for this kind of thing even if there was a "correct" but more complicated way to do it.