The uniforms of Xi 'an Middle School in Shaanxi Province can be bought in uniform shops or clothing markets. When choosing the purchase method, you can consider the following factors:

* Convenience: If you are in the local area, it may be more convenient to go to the school uniform shop; If you are not in the local area, you may need to buy online.

* Price: Compare the prices of different products or sales channels and choose the method that best suits your budget.

* Quality: Some school uniform shops may only provide certain types or brands of school uniforms. You can compare the quality of different products or sales channels and choose the one that best meets your needs.

Please note that in order to ensure that the purchased school uniforms meet the requirements of the school, it is recommended that you consult the relevant regulations of the school before purchasing.