For wheels which are much more readily available, consider fitting Volvo rims to the Twin Cam spider. They are a loose fit - maybe 1mm oversize, easily packed with sheet metal prior to welding and not too great a gap to bridge. The wheels to use are Volvo 164 sedan 15" X 5" wide or 165 wagon 15 X 5.5" wide. These are a modern safety style rim with the bead groove for tubeless tyres and therefore do not look entirely original. It may be a bit embarrassing to admit to using Volvo parts on an MGA but it is a convenient source.