Tried a couple of helmets at XXL and they are not bigger enough, can't find any larger than this.... does anyone make bigger helmets ? measured at 64cm so at the top of most size charts for XXL

 I am similarly afflicted. You need to keep trying different brands of helmet until you find one that fits. In extreme cases you could alter the foam liner of the helmet a bit, which will defeat some of the helmets protective abilities.

Try taking the cheek pieces out - many just unclip/pop off.  This gives a much looser fit.  That is what I have done with my Wulfsport XXL helmet.

Thanks, tried that with the wulfsport, but it was more sort of sitting too high on my head... have now got an Airoh XXL TRR S that fits well, but 3 times the price !