I had a Miller furnace installed as a replacement unit aprox. 2 yrs. Ago. It has a filter that looks like a piece of very thin sponge and I have no idea where to find a replacement. I have inquired at Home Depot and Lowe's to no available. Thought I had found something but it was for an air conditioner and not it would work. :(
Any suggestion on where these might be available?

If you go to your phone book and look up heating air conditioning wholesalers, and take that filter with you, most of them stock the mesh type filter media... you buy it by the sheet and cut it to the size that you need...