HI MIKE HUMPA TROLLEY WHEELS ARE AVAILABLE
ONLINE IF YOU DONT MIND IMPORTING FROM USA
TYPE IN BEACH CART AND LOOK AT OTHER ITEMS THEY LIST CAB HOLDERS ETC. SOUNDS LIKE YOU JUSY NEED A TYRE THOUGH I THINK TRONIX ARE DIFFERENT BEING GLIDER WHEELS
Is that the Humpa lumper one with the grey tyres?
looking at those it looks like it's a split rim with three bolts to hold together.
Do they have a inner tube or just seat like most car tyres?
If can get it apart/inside can bond/glue a patch from inside to seal it.
Something like Tiger seal/polyurethane glue would work as bonds like poop to a blanket but stays flexible.
Something like a thick piece of inner tube would work.
Once on compress with likes of one of those speed clamps
THE HL TYRES ARE CCOMPETE SEALED UNITS IN SPLIT RIM WHEELS BUT WHETHER SONIK TYRES ARE INTERCHANGEABLE WITH HL WHEELS I DONT KNOW/ TJE WHEEL TO AXLE ARE CERTAINLY NOT THE SAME BUT HAVING SAID THAT A LOCAL ENGINEERING XO COULD PROBABLY ADAPT THINGS FOR YOU