I'm the biggest cheapskate around, but for what one gets, the turf tire package through Hoye is about unbeatable. The rims are custom made so the backspacing is correct. The center hole is the correct diameter. They are brand new. Price? 600 bucks, SHIPPED. While that is a lot, price a set of new wheels anything remotely like what they offer. The rears will be about $100 each, at a bare minimum, and either need to be hogged out with a grinder in the center, or will be larger than is correct. You may have to grind or drill the bolt holes, too. You would still need to ship them, too. However, the rears are probably doable on your own, though from new parts. Used wheels that would fit as Hoye's product does are fairly rare.
The fronts...not so much. You can perhaps find a wheel of the right diameter and width to match the lawn mower tire. You can maybe even find that with a bolt circle to match, but they will be very highly offset, and won't fit properly, if at all. So you would be stuck buying a factory wheel from....somewhere. There aren't any on eBay currently. Could you do much better than $100-125 apiece on them? Probably not. and unless one lucked out and found them locally, they still would need to be shipped.
So, somewhere in the neighborhood of $450 plus shipping on heavy steel wheels is as cheap as I could reasonably see someone sourcing their own new wheels, which will not match one another and likely require modification, if they work at all. Shipping seems like it would have to run $75 to $100, so a person would be within spitting distance of getting properly fitted, matched wheels shipped anyway.
Now, having said that, if I ever find a little Yanmar for cheap that is missing the wheels, I'm buying it and cobbling something together out of my graveyard of Chevy wheels. But if I had to buy new rims anyway, and wanted turfs, I would just bite the bullet and order from Hoye.