The following keywords may be useful in the UBC Library Catalogue:
Use quotation marks if you are using a phrase that is two or more words long (e.g.: "first nations", "indigenous peoples")
Use a question mark to truncate a term, which will allow you to search multiple words with a common root at one time (e.g.: aborigin? will search aboriginal, aboriginals, aboriginality, etc.)
Try the phrase "First Nations Author?" plus your topic in the UBC Library Catalogue to find works by aboriginal authors.