Thanks for reaching out. We do sell replacement bases separately but color options are limited. We do not have an estimated back in stock date for colors not listed. Below is a link to our replacement bases to check out what we have available.
Link to Replacement Bases
If we do not have the color you need the best way to get that color would be to purchase a fitted sheet (base + zip sheet) and have the extra zip sheet.
Link to Fitted Sheets