welcome back
+4s from the 60s were fitted with either knock off wire wheels in various widths (but usually 15 x 4.5 or 15 x 5) , or 4 bolt steel wheels (15 x 4.5)
I guess you are looking for the look of the Jaguar D type wheels of that era , these were alloy , not steel, and are horrendously expensive even if you can find them.
It seems as if your car is currently fitted with 4 bolt hubs and steel wheels? If so your I think you have a couple of options ;_
1 Convert to splined hubs , not cheap but will give you some option with knock off wheels , be they alloy or wire (I have never heard of knock off steel wheels)
2 Use alloy wheels on your current hubs (probably your cheapest modification)
I believe that some of the UK racers are currently using an alloy 4 bolt wheel that looks very similar to the old Dunlop style wheel ( Google pictures of Billy Bellinger's Cosworth powered 4/4 ) I think these are available (if expensive) and may give you the look you are seeking
Good luck
