EdgeStar does not manufacture or sell an inline water filter, nor do we recommend a specific brand for usage.
That said, any inline water filter with 1/4" inlet and outlet will be sufficient. There are plenty of options available online, at local hardware stores such as Home Depot that will work - just search or ask for a "1/4" In-Line Refrigerator/Ice-Maker Water Filter."
Sample photo of inline water filter below: