Replacement window latches can be bought in hardware stores or online. Hardware store websites offer them, as well as more general websites such as Amazon.
Many large hardware stores with websites sell window latches online to be picked up in-store or delivered, as in the case of Home Depot. The store has various types of window latches, such as sliding models, brass casement window locks and vinyl tilt latches.
Another example of a hardware store which sells replacement window latches is Lowe's. The online shop has a range of window hardware including security bars and guards, as well as window latches.