No way legally other than purchasing them from Cisco, unless you or your company has a CCO account (SmartNet on one device, reseller) or if you know a CCIE---in both cases, one can get access to any IOS for free.
Illegally, but Cisco won't care---IOSHunter---Cisco won't care because only deferred releases are available this way. Cisco doesn't even offer deferred releases on their website.
If you need an IOS for CCNA studies, then you'll likely need 12.4, which is not deferred. IOSHunter MAY get you one of these...
/
tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!