Yeh, try and get em from the likes of Brian James and they're circa 100 for four. The net/ebay will be your best bet. Bear in mind breaking strains when ordering.
Mine are ones that were designed to hold a marquee down. 1.5 ton breaking strain. You need to be careful with rathchets. If you use 5 tonners and rachet em right up, you end up bending steering racks and wisbones. Aways do each wheel individually with at least one on a front wheel and one on a back.
Machine mart do soft straps that go over the wheel.