St. John's used to be on Carling at Broadview, intially under the Dominic's label. Brian Dubbldam worked out of there. Dominic's website says that they are presently operating entirely online.
St. John's did carry band gear (lots of Yamaha, Fender, and Line 6), but seemed to deal primarily in high school band instruments and sheet music. I know we rented our younger son's trombone from there when he was in band, during middle school and early high school. Granata also carries lots of sheet music and is just a little further up Merivale from where St. John's was. I've never been to the Orleans location but the South Keys L&M carries plenty of books and sheet music, as does Steve's downtown. I suspect that the rental market kind of dried up for St. John's as more and more band instruments began showing up on Kijiji when junior decided that maybe playing clarinet or saxophone in junior band wasn't for them. And, considering the total cost we paid to rent the trombone that sits gathering dust these days, I could have gotten a better instrument on Kijiji for less than half that. So, between the rental market drying up, and many other places and ways to get sheet music (including simply downloading and printing out public domain stuff), selling the odd Yamaha acoustic or full retail-price Boss pedal was not going to pay the rent and salaries. Perhaps there could have been a better location, but that may not have been enough. When they were on Carling, at least they were just around the corner from Notre Dame and Nepean high schools, that probablygenerated enough business to cover overhead and maybe a little more.
My first guitar came from Sam's ABC, down on the market, back when it had more pawn shops than chi-chi ristorantes, bulk food stores were known as "biscuiterias", Freiman's (now The Bay) had their fabulous malted milk for 20 cents a glass in the basement, the Lafayette had draft for not all that much more, and Irving Rivers himself really DID corner the market. Sam's eventually moved up to Bank, near Alta Vista, very close to where L&M eventually opened up. Sam's son Phil was in my cub scout troop.
International was briefly situated in a basement location within St. Laurent shopping centre, before moving to a location just behind the main postal station at Riverside and Industrial, and eventually out to a nice location on Strandherd in Barrhaven. Pity they closed. They carried a nice selection of gear.