If you're looking for Sediment filter replacements for standard size 10" housing reverse osmosis water systems, you can easily buy a pack of 6 online. Typically, pre-filters  and Post-Filters in  RO systems last around 6 months between changes, while RO membranes can last for as long as 2 years. 
 
The High-Grade 1 micron high-capacity polypropylene sediment filter plays a crucial role in removing larger particles and suspended matter such as dirt, silt, rust, and sand from water. It protects and extends the life of the membrane and the entire system. It's recommended to replace this filter every 3 to 6 months, depending on the quality of the water source.