To be honest, I'd think AAT level 2 and 3, learn some bookkeeping, nominal accounts, sales ledger, purchase ledgers, etc
Should only take you like a week to learn the basic stuff and have a practice and when your confident, go volunteer at an accountancy firm and ask if you can do small roles for them for free.
If they see your good enough, they may ask you to help on more roles but your limited to do only so little, just bare that in mind.
Finding someone to sponsor you is difficult, even high grades aren't enough anymore. Experience is more the judge factor now and most people are equipped with experience.