Multiple ways, but none without setbacks.
Glyph of Warding - Takes 1 hour to cast and two spell slots, but with enough time to prepare, it can break encounters. At level 20, my players used it to chain cast True Polymorphs on themselves, really amazing.
You can store a prepared spell of 3rd level or lower in the glyph by casting it as part of creating the glyph. The spell must target a single creature or area. [...] If the spell requires concentration, it lasts until the end of its full duration
Twinned Spell - You can dupe a single-target spell when you cast it. Basically, you can Suggest two enemies to run away as far as they can.
When you cast a spell that targets only one creature and doesn't have a range of self, you can spend a number of sorcery points equal to the spell's level to target a second creature in range with the same spell (1 sorcery point if the spell is a cantrip).
Wish - Use it to cast Glyph of Warding. Major difference here is simply bypassing the 1 hour cast time.
The basic use of this spell is to duplicate any other spell of 8th level or lower. You don't need to meet any requirements in that spell, including costly Components.
Simulacrum - Have a clone of yourself doing spells alongside you! You can even give it Magical Items so that you don't worry about spell slot regeneration.
The simulacrum is friendly to you and creatures you designate. It obeys your spoken commands, moving and acting in accordance with your wishes and acting on Your Turn in Combat. The simulacrum lacks the ability to learn or become more powerful, so it never increases its level or other Abilities, nor can it regain expended Spell Slots.
Other answers have mentioned having NPCs (either hired, or dominated), and they cast spells as well. It is an option, yes, but they won't have the same spells you have, so maybe not applicable.