Upwork freelancer needing to source UGC content for client $5000 budget

Hey reddit familly, I'm a freelancer on upwork. I have a client who asked me to source UGC content for their brand with a budget of $5000.

1. How do I source content on marketplaces like billo without them knowing?

2)How do I get the budget from my client and pay on marketplaces without them knowing?

Looking forward to hearing your recommendations! :)