...for fear of being vilified, I nearly haven't posted this...but Im going to anyway!
My 'parts-bin special' has a home-made seat and the hinges are...well...door hinges that I had to hand in the cellar. The retaining pins are six inch nails cut to size and peened over.. But then, it's not a restoration, it's a cheap and cheerful build from spare parts!! On the US site there are some nice home- made brackets on some builds- I've seen lumps of aluminium machined to size, but doesn't really help for a restoration. So lots of ways to do it to get you on the road and give you time to source an original set..Good luck!