For Business/First awards, you can't be too choosy, not this close in, but they do exist since March is still low season.
My results are in the title above. How you get from those places to London, I'd look at budget European carriers to link you back to London.
I also checked MAN, DUB, MUC, CPH, WAW, IST, ROM, MAD, SMP, TGL, VIE and GLA.
I found that i can go through Frankfurt, but can i get another flight for free as connection via Frankfurt? do i do multiple cities when I look up the flights?
Yes. The overseas leg is critical path. A couple months ago, I got SFO-FRA-NUE. I've also gone FRA-STR and FRA-MUC.
I just noticed that UA's n/s SFO-CDG service is back. Unfortunately, 3/11 is not in the timeframe for the 50-100% RDM bonus that's good for travel in 4/11-5/31.