I'm sure you can find a Cambridge packet somewhere on eBay/amazon, but they will most likely be pricey since the company no longer sells them. If you upgrade to ultimate+ though you can get all questions with explanations!
Ultimate+'s drills are the replacements for the Cambridge drill sets. We'll have LG and RC sorted out within the next few weeks; LR is already out there.
The Cambridge drills don't exist anymore, but 7Sage's Ultimate+ package has drills separated by PT#, section, question type, etc. https://7sage.com/enroll/