If you have installed Extended Block Shapes and Blockus mod, you may optionally install "Extended Block Shapes - Blockus" mod based on that two mods, so that extended shapes for Blockus blocks will also be added.
Note: There are no specific groups for these blocks. Therefore, to find these blocks in creative inventory, you need to enable "Add to vanilla groups" in the mod options of "Extended Block Shapes", and find these blocks in Blockus item groups.