These guys claim to use Walther barrels:

Precision Rifle Systems

They might not supply barrel blanks, but should know who the agency is! My .416 Taylor is built on a Walther barrel, faultless. I'll ask Vic P_ where he got it from next time I see him, but that was a few years ago now and our importers have had a shake-up or two over the last decade, as you know!