The WiFi modules on most of the Chromebooks I've seen in the past are actually fairly easy to replace, so that might be a consideration if we knew the make and model of yours.
Otherwise, an internet search for "USB WiFi adapter for Chromebook" should give you plenty to work with. A user on Reddit has verified that this one from Amazon works with his Acer Chromebook.
[link|https://www.amazon.com/Wireless-Adapter-150Mbps-Set-Top-Raspberry/dp/B01KWQAQ00/|Amazon.com: Wireless WiFi USB Dongle Stick Adapter RT5370 150Mbps for MAG 254 250 255 270 275 IPTV Set-Top Box, Jynxbox, Linkbox, Raspberry Pi, Pc Laptops Desktop, for Win7, Win8, Mac OS, Linux : Electronics|new_window=true]