First, what sort of creep takes the oven racks when they move out?
Sounding off complete, if this is a rental, it is the landlord's problem 100 percent.
But trying to get many landlords to actually take care of a problem like this can, at least in my experience, be a tedious and frustrating problem. If your water does not work, they gotta do something. But many may not move too fast to correct your absent oven racks.
Like the idea of getting the landlord to grab one from an empty rental if there is one available, but that may not be an option.
If this is a rental with several other units, there may be someone who has two racks in their oven and never uses more than one. Maybe you could ask about borrowing one. Particularly if you need the oven for T-day.
If this is your own place would try to get the model number, or at least the measurements of the needed, and see if you can find a replacement, even on the web.
As a last resort there are folks who weld things together and could probably make one or two.
That's all I got. Good luck.
Before criticizing a person, walk a mile in his shoes - then you are a mile away and you have his shoes!