For anyone looking: after a week scouring the internet and getting nowhere, Elektron support were able to point me to this Swedish site selling the exact PSU i was trying to find (Mascot model 8810, 6VAC, 3.2A). It’s the only one still being made that’s suitable for mk 1 silver boxes, as far as i can tell. Thank god for Norwegians!
And you need to buy this plug tip with it: