As you know, Eric, the 400 series have become something of a rarity these days and very few breakers yards, at least in this part of the world, keep older vehicles such as these. You may have a better response/luck from the 400 Wants section or take your chances on eBay.
Also see list of
UK Volvo Breakers thread.
Failing that I may have a pair of RHD S/V40 wiper arms in my shed (I will need to find them) if you wish to experiment with those.