Wow, that is thin.
I know people custom make spokes for veteran machines over here. I'm guessing there may be 'Wheelmen' members over your side of the pond who do similar stuff.
Nipples would have to be custom-made too.
You could always build up a racing wheelset with spokes of a different size. A fun, sometimes frustrating, but ultimately rewarding and satisfying experience.
I'll be building a set for my National soon, admittedly not as rare a beast as yours (it's a 1911 Model 132) but I'm so looking forward to riding it, hopefully this year too!