You can still get the free bundle of assets at this URL : scirra.com/freebundle.zip
The Beginner's guide to Construct 2 does contain the assets within the tutorial itself for you to right-click and download.
The platform tutorial relies on assets which are provided when you own a license.
Go to your downloads page and click the link "Download included asset bundle" underneath the "Download" button of your license if you have one. - scirra.com/store/downloads
If you do not, it is up to you to use any other type of assets to complete the tutorial (which is the basic of how things work in Construct).