I made exhaustive enquiries about 20+ years ago for my DB2Ds, all the manufacturers I contacted said that they used to produce them, but moulds were lost or destroyed years ago, I used to find scrap Plowmates etc as a source of tyres, but they have a value of their own now, so that source has more or less dried up. As for tubes, I think I may be able to help with a used one, If interested let me know and I will look.
Chris