As I have a set of wirewheels Triumph Tr6 with the hubs and different pattern 4 x 114.3, I was searching for adapters to adjust into the MX5 pattern 4 x 100 and came up with this company :
http://mywheeladapters.com/
For 4 lug Hub Wheel Rim Spacer/Adapter 4/100 to 4/114.3 and postage to Holland I have to pay about 105 britisch pounds.