3 themes in a pack are now available individually. Thus you can save a lot by purchasing the Pro Pack here which includes all 3 flat themes below and other free themes.
Cerium D(8 styles) – https://www.sultantheme.com/product/cerium-d-vb5/
Xderium (5 styles) – https://www.sultantheme.com/product/xderium-vb5/
Trixerium (5 styles) – https://www.sultantheme.com/product/trixerium-vb5/