UBC's Library, Archives, and Rare Books & Special Collections (RBSC) are each separate institutions. RBSC Archives holds archival materials collected by UBC, while the UBC Archives holds material created by UBC departments and professors. You will have to search each institution separately to find all the primary source materials held at UBC.
UBC Archives has put together a guide to finding First Nations Historical Resources in the UBC Archives. Note that further searching within finding aids may be necessary to locate this material.
UBC Rare Books & Special Collections
The best way to search for this material is to use Rare Books & Special Collections database search. RBSC's search does not use phrase (e.g. "residential school") or truncated (e.g. residential school?) searching. Try a simple keyword search (e.g. Residential school).
How to search the UBC Archives, Bibliographies and Reading Rooms catalogue from the UBC Library website:
Or bookmark this link: webcat1.library.ubc.ca:7108/vwebv/searchBasic
UBC's Institutional Repository, cIRcle, holds full text of UBC theses and dissertations. Some of these focus on Musqueam and local relationships with First Nations peoples. You may also be interested in broadening this search to include all of UBC's Open Collection by adjusting the filters on the left side of the page.