International factoring of foreign receivables is a specialty. The purchase of invoices due from foreign companies or governments is done by factoring companies having the ability to do the documentation, underwriting and follow up on a transaction. The factoring company doing the work usually concentrates solely on this sort of funding.
Unfortunately there are significant barriers for this type of invoice financing. One is historical experience, has the transaction been handled successfully already? Another is country of origin, not all foreign countries can qualify for this type of financing. Invoice factoring companies financing foreign receivables will only work with a business producing a minimum of $200K of invoices monthly. In order for it to be worthwhile, this amount of billing is a starting point to getting funded. The degree of effort involved makes it unlikely that smaller monthly amounts will be worthwhile. So companies needing to do invoice factoring internationally might need to search elsewhere for other resources when just starting out.