Perseverance is key here. Try every day and also with different agents. You never know when inventory will open up. Sometimes you have to be flexible and willing to make 2 or 3 stopovers. Have the agents check with partner carriers and especially to secondary European cities (DUS, MAN, CPH, CGN, etc). and connect from there. Sometimes inventory is better if you connect through Canada. Once you get your foot in Europe intra-European connections are easier to find. As your travel day approaches inventory can open up and it has happened to me 1 day before my trip on AF for 2 business class seats. Needless to say, that approach is risky. I was able to do it because my companion was Platinum and there was no fee to get tickets reissued. We already had seats confirmed SFO-EWR-CDG but wanted to try for the nonstop SFO-CDG. Good luck.