Hi, I want to multiclass a paladin and a sorcerer. My DM told us that your chars will reach lvl 8 before the final fight so i would love the idea to be able to cast some 3rd lvl spells. If I have a paladin lvl 5 and a sorcerer lvl 3 my character would get two 3rd level Spellslots that i can only use for smite. 

Is there an option to unlock one or two 3rd level spells with a feat or magical item? The campaign won't last long enough to get the paladin to lvl 9 nor the sorcerer to lvl 5.

Would it be possible to get a 3rd level spells with an other caster class while i keep the 5th lvl paladin?

Thanks for your help!

I think you've got some tough decisions to make.

There's no way I know that will give you 3rd-level spell slots from a feat or magic item. If you have specific spells your want to cast, you might find something like wand of fear or wand of lightning bolts .

If you really want 3rd-level spells and not just slots (which can be used for upcasting not just smite btw), you're going to have to go sorcerer 5. If you only want paladin 5 for extra attack, you can always quicken a booming blade.

Thank you! I'll try booming blade and quicken spell instead of getting my paladin to lvl 5.

I want to take divine soul for thunder step and mass healing word or revivify.