1. physical bookstore: You can go to the local physical bookstore, especially the bookstore selling educational materials, and ask them if they have the math exercise books you need.

2. School or educational institution: Contact your child's school or local educational institution and ask if they have any recommended textbook suppliers or exercise books that can be purchased.

3. Online second-hand bookstore: You can try online second-hand bookstore or second-hand goods trading platform, and sometimes some people sell second-hand teaching materials.

4. Education Press website: Go directly to official website of the relevant education press, and sometimes they will offer online purchase options or guide you to the nearest point of sale.

5. Educational resource websites: On some educational resource websites, you can find digital teaching materials or exercises, which may be provided free of charge.

6. Ask the teacher or other parents: Please talk to your child's teacher or other parents, who may provide useful advice on purchasing teaching materials.

Please note that the availability of books may vary by region and supplier, so it takes some patience and effort to find the required teaching materials.