Hasbro started the Build-A-Droid (BAD) figures in July 2008 with each carded figure in The Legacy Collection. When all figures in a wave were purchased, you had enough parts to assemble one, or in some cases two droids.
In addition to that, Hasbro released Walmart exclusive 2-packs under the Droid Factory name, which also contained droid parts.
Droid Factory 2008 - 2010
Complete release chronology 2008 - 2010