Have you already installed this sink? There are some sink brands that include the grid for free, like Kraus. This Kraus sink is similar in dimensions as the Mirado 310, and comes with sink grid and drain strainer for free.

If it is already installed, and the company doesn't provide the grid, then I don't know how to find a grid to fit. But you know what - I am not that big enthusiast of sink grids. They need to be cleaned and get gunk in all the corners, things fall through them, sometimes the feet's padding wears off and the feet scratch the sink, and you might as well just live with the stainless steel sink's scratches than have to deal with the grid. Just MHO.