Bottom bracket spindles are hardened steel, and don't easily strip. Check the threads on the mounting bolt or nut as they are more likely to strip than the spindle. They're also cheaper and easier to replace.

N.B. if you rode any distance with a loose crank arm, there's a good chance the arm may be damaged and will no longer stay secure on the spindle. Look for gouges or other damage where the arm mounts on the spindle.