It was suggested I contact the Amazon Message Center after purchasing this product to inform the vendor of the size. The existing filter is 28"x30"x7/8". I would like the same size of new filter.

You should be able to get this filter at any home improvement store.

I can't stand it when these manufacturers build an air fiter opening for a size of filter that's hard or expensive to get! You can try to contact the manufacturer to get air filters or if they know where you can get them. If they can't help you (and they built it, they should know!!!) try contacting a local air filter service company for a special order. And if they seem too expensive call around for a better price or locate them online.