Almost any custom frame builder makes them, like Mercian and Waterford. There are a lot of smaller shops out there too, just not that well known. I can't remember most of them off memory.
Production frames are a bit trickier since most are partially welded, with some lugged parts. Rivendell is the most infamous, SOMA makes a couple I think (from Taiwan). I don't really know too much about 100% lugged and brazed steel frames that are stocked and available on short notice.