Need to find an adapter for a foreign faucet?

We purchased a faucet on Ebay that is considered European. It comes with its own custom water lines (the braided hoses) which are m/f with a 5/8 connector. Most water lines are f/f so this is already a problem. on top of that, our water spouts are 3/8. We cannot find an adapter that would fit a 5/8 out and a 3/8 threaded in for Iron. We also cant change the water lines as they are custom fit for this faucet. We are having this issue with quite a few faucets we have looked at for our vessel sink. We went to Lowes and took out out of the box even, and it too is different. I thought 3/8 was standard so Im confused as to why even US made would vary. We really like the faucet and are trying to find a way to fix this issue. I am not a plumber so I apologize for the jargon. I have contacted the manufacturer and all they can do is issue me a partial refund which doesnt even cover the cost of a new one nor solves the problem.