190mm x .03937" = 7.480" which is unusual, could they be 7.25", which is a standard 5/10 lug dimension? Anyway, if this the case, I presume they are 20" tires. The only standard replacement is another of the same wheel.

Another option, if they exist in Oz, would be 22.5" tubeless rims, which came out in late '50's trucks when tubeless tires first became available for trucks. They used to be common in the 'states on farm trucks, so that might the best place to look. One can mount up to 9" x 22.5" tires on these rims.

Good luck,

Ed

'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.