ContractingNoob

Hi all, I currently help manage presales/proposal responses for an international company, primarily UK-based. They're trying to grow in the US, and they're looking at trying to expand into federal contracting. We have a large list of UK public sector work, but I explained to them that the US gov wants to see US past performance. I suggested that we look into subbing as a way to gain federal experience because we could not feasibly win on our own yet. My question is this: how do we find subcontracting opportunities? Is it a matter of meeting with primes and contacting them outside of these websites? We are in a weird spot because we can't classify as a small business (due to our legal structure) nor do we meet any 8a/Hubzone/etc requirements. I have looked on subnet and sam.gov but am struggling to find a concentrated view of subcontracting opportunities that we could reasonably go after. With that in mind, where would you recommend I get started? And is this even worth pursuing for us? Thank you in advance for any help - it's greatly appreciated. Cheers, Christopher