I think many headlamps keep the low beam on when turning on high beams.
What you might be thinking of: HD makes a harness (about $30, probably) for non-CANBUS bikes that lets the
passing lamps stay on when the high beam is on; IIRC, the dealer can program CANBUS bikes to keep passing lamps on with high beams.
When I replaced the halogens in my '11 SERGU, I went with the HD Daymakers. They were very bright. Sadly, I've heard the newer Daymakers aren't as bright...but that might have changed. Of course, they have the Harley tax on them, so you can definitely get a better price. If you decide to go with Daymakers, they are available through the 20% off dealers.