Wheeleez Wheel Conversion...Help Needed

Hi all, I'm hoping to find some help from the forum once again. I have an original Wheeleez Beach Trolley with the big balloon beach tyres. I want to fit a standard hard rubber utility type wheel to the trolley but several problems arise from what sounds simple. The European distributor is based in Barcelona and provides a conversion kit but the axle on the conversion kit is 20mm diameter......the axle on my trolley is 12.7mm !!! The axle on my trolley has a ridge onto which the ballooon tyre hub locks and therefore there is no hole in the axle into which a split pin ring could be fitted to hold a wheel on the axle.......even if the diameter was right. The split pin ring type fitting is a fairly standard method of fitting a wheel on most carp type barrows, match type platforms, seatbox trolleys etc. Any ideas, previous experience of such a conversion, a wheeleez type trolley with hard rubber utility type tyres for sale or even someone who could, for a price of course lol, make one to fit. Not being at all handy or even reasonable at DIY there's not a chance I could manage such a conversion, even if I had the facilities to do so. I'm open to all and any help offered. As always many thanks for any insights or help.