This assumes you already have the initial pack loaded & need what used to be the 3 additional "Jam Packs"…
Would you consider 5 bucks worth it, to stay on Garageband 10?
GarageBand menu > Download More Sounds
If you previously purchased this content, select Restore Purchase to install the content
[I'm not certain if 'previously purchased' includes the iLife purchase, but it would be worth testing]
Source : Apple KB - Expanding GarageBand for Mac (v10.0) content with an in-app purchase
Alternatively, if you don't already have the first Jam pack fully loaded, this might be a solution…
Open GarageBand and either create a new project or open an existing one (don’t worry, we won’t be making any edits to the project).
Navigate to the Loops section by clicking on the Loops button in the lower right corner of the application.
Next, you have to find a Loop that GarageBand knows exists, but has yet to be downloaded. It appears Apple let GarageBand know that there are other Loops in existence that were not opted to be included in the base install of the application.
The easiest way I’ve found to do this is to first Click on the “Rock/Blues” category to narrow the number of Loops displayed, and then find the “70s Ballad Drums 01”; which will appear slightly greyed out and its icon will be an empty box with a dashed border.
Double-click on the missing Loop, and a rather large (and semi-confusing) dialogue box appears. In short, you want to select the “Download Now” option and click OK.
Next, you need to open the App Store application and navigate to the Updates tab. Once there, you will find the ‘Update’ to GarageBand nestled under Software Updates for OS X. It is entitled “GarageBand Instruments and Apple Loops 1.0”.
Even though the large dialogue box in GarageBand said the update would be downloaded “now”; when I went through this process it did not automatically start the download. This may be due to how I have automatic updates turned off on my machine (for development reasons); so it may have already started downloading for you at this point, but just make sure the 'Update’ is downloading and you’ll be good to go!
One quick thing to note: you will have to quit and reopen GarageBand before you can start using the new software instruments and Loops that were downloaded.
Source : How To Update GarageBand with Nearly 1,000 Instruments and Loops for Free!