Or leave it as it is, and just provide a USB socket in your device to plug a WI-FI stick in.
If you really need ICs, contact Ralink, Atheros, Broadcom and the like. Be warned, those ICs aren't intended for DIY usage, are hard to find in small quantities and it is hard for a hobbyist to find enough information about a chip or chipset (including firmware license) to get on running from scratch in an own design. This is a high-volume market with a lot of secrecy around it.