Not a 44mm headtube*, but a Ritchey logic (and a respray because I hate grey).
As for custom, Mercian defiantly do lugged 631 frame and forks <£1k. Although the extras list rapidly adds up (lug lining, painted panels etc)
*I’ve still got 1″ headtubes on some bikes, yes 1.1/8 isn’t as stiff as 1.5 or 1.25, but it’s not the be all and end all, Cervelo still don’t use oversized tubes for example. And Sam (singular) makes good case for them on the Swift, because you can’t get 44mm downtubes there’s little point, as a stiff headtube in isolation doesn’t add anything. And 44mm headtubes on road bikes look naff.