Hardware Store? Not very likely, unless it is one of those Industrial Supply Hardware Stores. And even then, they would only probably have a generic spring you would have to trim.
It is possible the Spring has lost it's tensile strength for some reason. Remove the Magazine Release Assembly from the Frame and inspect it for wear or damage. Replace any suspect parts with the appropriate parts from Taurus. The Pin in the trigger guard in front of the Magazine Release, retains the whole assembly. The Taurus Manual shows how to remove it for side-switching.
If you are not comfortable doing that, send your Pistol off to Taurus for repair, or seek the services of a competent Gunsmith, familiar with the design.
The Magazine Releases on all of my PT900 Series Pistols have been fine over the years and have not worn out at all, so this is not normal! Even my well worn PT92's magazine release is still good. If any of them were to wear out, it would be that one, as many miles as I've put on it!