This site is a Wheel Bolt Pattern Cross Reference Database and Conversion Guide and compares your wheel specifications (number of studs, PCD, centre bore etc) with wheels made by or used by other manufacturers. It is US based but may be helpful.
Good idea Conti as there are so many variables out there. If anyone gets stuck though looking for a tyre or rim send me a pm. We worked out a few alternatives when I was in the shop and did quite a few older cars, often using tyres that normally wouldn't be thought of. Plus one of my contacts is a rep for a company that handles a lot of the older or as i call it weird sizes. I had one of my dealers ring me today asking for a 10,00x20 luggy pattern for a ww2 army trailer and sure enough they had them. Recently I have had a few dealers show me old wheels they have been storing so can always keep an eye out for a particular wheel. Rollydog