Makes sense to me. I still have not heard from anyone if they have ever added an extra set of wheels to a John Deere 42" deck? Anyone?
I have not done it myself but have read a lot of threads on it. If you go to Amazon.com and search in 'Patio, Lawn & Garden' category for "mower deck wheel kit" you can see some of the choices available.
There is the Poulan Pro GWN42 wheel kit, as well as the Arnold OEM-190-183 kit. Both of these kits include two wheels and the brackets. You may have to do some slight bending/shimming/fabricating with additional steel in order to make these fit your deck perfectly.
How handy are you? Do you have any metal fabrication skills and/or equipment? If you can bend a piece of metal and drill holes in it, you can probably just order the wheel and an axle bolt, and have a series of holes drilled to set the height. Paint bracket with Deere yellow which is available in a rattle can.
Or, if you have used mower parts available, you could find a rusted-out deck at a mower repair shop or dealer and harvest a set of wheels and brackets off of it.