Kalin,
If machining is an option, then maybe you can modify some 140 front spindles to be metric -- obviously welding would be needed at a minimum. If metric, you can use the hubs that Deere makes for later tractors. The part number is AM140109 and GreenFarmParts.com has them for about $97 each -- more than when I did my conversion but still within reach once you have metric spindles...and you can use the correct metric lug bolts without any modifications to the bolt holes on the rims.
The bearings in the AM140109 hubs are identical to the standard wheels with integral bearings, so they do not increase load capacity. The "high speed trailer hubs" as used on the one inch spindles are rated at much higher loads, but you are not likely to exceed either bearing rating even if you have a FEL or similar attachment on a 140 class garden tractor.
Chuck