Furnace filter for Carrier model 58DHB055-CC

I'm trying to find air filters for a Carrier model 58DHB055-CC. Evidently there are supposed to be two filters that sit in the return-air plenum above the blower in a V configuration. Is there a part number for this filter? Perhaps a larger filter that can be cut down to size? I haven't been able to find any information about this furnace on the internet. I don't even know how old this furnace is. Presently, the furnace is running without any filters at all. (Is this a terribly bad thing to do?).
Bob D.

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