Ask HN: How do you procure data for software tests?

I am building a product in the procurement space, and would like good data to test this with – e.g., purchase orders and invoices that have some erroneous entries, invoices that don't match purchase orders etc. What are the options I could use to generate this dataset?

Also, I want to probably use data to demo the solution to prospects, and I'd like to have this datasets generated specifically for each demo (i.e., if a customer only deals with services, there is no need to show him demo data that has inventory movements in it, really).

Any opinions appreciated!