The standard minor wheel has an offset of 28mm. You may find some Vauhaull steels will fit. The trouble is that the wheels that may share the 4" pcd will have the wrong offset. This can be a big problem on the front,but less so on the rear. Talk to Compomotive as they will produce the wheel you want, although as you have already found out the choice of style is limited.
Standard IMP wheels were only 12" diameter ! Yes they are 4" pcd - as were Viva wheels of that era, also sadly only 12" diameter.
And I have sat my Traveller on a set of 12" Mini Minilites I have in stock - but it just looks stupid ! Partly because the tyres are low profile - but mostly because the wheels are just too small.
15" Minilites look great on a Traveller - but cost a small fortune !
Try E bay - type in - Slot Mag, Cobra Wheels, Wolfrace Wheels or Shelby Wheels - eventually you will get lucky. You shouldn't have to pay much more than £100 for a set - I've already bought some this way.
Were they genuine 4" pcd - not just 100mm 'persuaded' to go on ??
Followed your pointer - they are from a Viva so correct at 4" - sadly only two of them, and only 13". But I will set up a search as you suggest - thanks for the tip !
I think that 13's look fine on a minor if you don't get too low a tyre profile. I used to run 6x13's with 185/70's and they looked good.
Check out this site as you can work out easily the rolling circumference etc to achieve the best result, and compare different wheel sizes etc.
I think the stud will be bigger - I used Viva 12" wheels on my Autocross Mini long before 12" wheels became standard - and I had to make up special wheel nuts from bigger hex bar to suit the locations on the Viva wheels.
Slot mags use sleeve nuts and washers, so the hole size is normally the same no matter what wheel you get. Therefore if you buy the correct nut, this fits both the hole and the stud. I've fitted viva wheels with no problems before.
Check both these sites out for suitable nuts (great service).