How can I become a teachers istant? I'm finding it real hard to get work experience!!?

Hey- I have tried to get work experience with primary schools so I can become a teachers istant but i'm running into walls- as they have deals with unis or need a CRB check- but I only can get one once I'm a part of an organisation- is there any other way I get become a teachers istant? It's real frustrating -also how easy is it to find work as a TA?