I had the same problem! This is a little nutty of a way to go about it, but I happened to accidentally find out their sippy cups have 3s on them. I got a few from Amazon: Philips Avent Natural Trainer Sippy Cup with Fast Flow Nipple and Soft Spout, 5oz, 1pk https://www.amazon.com/dp/B075GXMNLL/ref=cm_sw_r_cp_api_glt_i_SN9WZGRNPXM5EBPEP3KG?_encoding=UTF8&psc=1