Igadevil has reviewed H.G.C.O.R.E. Kamen Rider volumes 1 and 2 on his blog. He has a ton of photos to share, and reviews every single figure – safe to say that it’s the most detailed review in English (maybe the world).
They’re relatively old sets, so you might have a hard time finding it outside of Japan. If you’re looking for them online I suggest eBay (make sure to check the eBay Stores as well), and newer sets can be found at HLJ.