I can confirm Sidearms was available at my local RadioShack up north
But was it available as a French version with a French manual? (Or was it a gray market item?) Do you have any pics?
Radio Shack in Canada was a different company than the USA chain and up here, many didn't follow the typical store design/catalog and brought in all kinds of games from different sources. I had to get my Mother to pick up the Turbo Sidearms for me during a trip to Washington state. I already had Sidearms Special, but wanted to see what the chip version was like, wanted a game I couldn't get otherwise and it was fun to play on my Express.
I'm pretty sure that NEC/TTi confirmed to me during phone conversions and letter replies that the third party games weren't available in Canada. I know WD definitely confirmed it and told me that they were working on setting up Canadian distribution connections (their Sega-CD games were available in Canada, but the early ones could have been imports). At least WD did direct-mail sales. Otherwise I don't know when I would have been able to experience Exile and CF2.
During a trip to Seattle, shortly after SFII' was released and during the week that EGM first announced that SFIIT was in the works for SFC, I found Exile and Vasteel at a game store, but only ad enough money to buy one. I made the right choice and got Vasteel, which received way more play time than Exile, which I eventually ordered direct.