Welcome to TTS!
I did some quick digging and used a '98 Burb for the search.
Part number for the Rear Gate Switch is 15687025 but discontinued.
Given the discontinued and apparent no longer available (NLA) status, consider a bone yard or eBay and include Tahoe and Yukon (and possibly Escalade) of the same year as part of the search as IIRC they all shared the same switch.
Alternatively, it is highly likely that a simple momentary switch will work in its place.