Hello,
If the webparts aren't available then you can simply install a new instance of Kentico, export the missing webparts from there and import them into your instance. Please make sure the versions are identical. If the webparts are physically on the filesystem there, then you need just to register them as any new
webpart. However I would suggest you to use the first approach as you need them to have the same codename if they are somewhere used already. You can also write us an email to support@kentico.com and we will send you the exported webparts via email.
Best regards,
Boris Pocatko