The only citation I can find for this story is from Jan of 1999 in the "weird news" section of the Houston Press:
Least Competent Teachers
*In November several teachers at Lindsay Thurber High School in Red Deer, Alberta, Canada, reacted to a bomb-threat note found in a classroom by sending students out to search lockers in a quest to find the bomb
However, I did come across a more recent story (from a couple of weeks ago) about Lindsay Thurber HS:
Fight between Syrian and Canadian students at Red Deer high school sparks protest
RED DEER, Alta. — Educators and RCMP are trying to keep the peace at a central Alberta school after someone posted a video on social media of a fight between a small group of Syrian and Canadian students.
The scuffle outside Lindsay Thurber Comprehensive High School on May 16 attracted online comments accusing the immigrants of whipping students and accusing school officials of not disciplining the Syrians.
More than a dozen people showed up at the school parking lot Tuesday to protest, including an anti-Muslim group called Worldwide Coalition Against Islam and another group called Soldiers of Odin.
Principal Dan Lower said most of the protesters have no connection to the school. Mounties were on hand as a precaution and regular classes were underway.
I found stories of more recent bomb threats (up to 2013). There appear to have been several at this school over the years; either it's a fairly frequent occurrence or there is just no other news worth reporting in Red Deer. But nothing about teachers sending the students to find the bomb.
"Hang on while I log in to the James Webb telescope to search the known universe for who the fuck asked you." -- James Fell