[barnstenchfartface]

The Rider Hero Series is, afaik, around 17-18 cm tall or thereabouts. So I think they're taller than the Spark Dolls. As far as a database of them goes, I don't know how complete it really is, but MFC's seems like a good place to start.

The Legend Rider History vinyls are from a line launched alongside Build that aim to release older main Riders with better proportions/detail/paint. Though whether they actually are better appears to be kinda mixed:

The Build RHS releases are all in the same style as these LRH ones.

As far as buying things, I can't really be too sure since I don't look at these too much, but Mandarake would probably be a good place to look. It often is, for most things.