If you are looking for a canadian store, futureshop and staples has them. They sometimes come with the hard drive and case while others might have the case only (and you would have to buy a hard drive yourself).
Also, many canadian online stores have them too like: NCIX
where you can buy a hard drive and place it in one of the enclosures.
There are many types of enclosures/case:
2.5" = usually for mobile hard drives
3.5" = standard desktop hard drives
5.25" = for optical drives (DVD/CD) and standard desktop hard drives.
Hope this helps,