Zinge Industries offer a pack of cinder blocks, however for 28mm they are rather large (20x11x10mm) which using my standard modern scale of 1/50 makes them a metre by half metre by half metre.
This is about twice the "standard" size according to Wikipedia. However they would do for slightly more industrial (ie 1980's Dockland) scatter terrain.
I used a Products For Wargamers MDF Scatter Terrain Base and used a razor saw to cut some of the blocks diagonally, this allowed me to get a bit of height, and "increase" the number of blocks.
Having decided on how the blocks would be arranged, I feathered in the base with the curved side of a half inch half round file.
I drilled three holes in the board and superglued three lengths of 1mm plastic rod as anchor points. Using MIlliput, I then bedded in and mortared the blocks in place.
Ground texture was the traditional Woodland Scenics fine ballast with added larger granite ballast over PVA glue.
The top surfaces was then sprayed with Rustoleum Rust effect spray. The bottom of the base was sprayed with Halfords Grey Primer and the top sprayed with some ancient Citadel Ogre Flesh.
The blocks were then painted with Citadel Mechanicum Grey. This was then dry brushed with a mixture of Citadel Mechanicum Grey and Citadel Terminatus Stone, working up to pure Terminatus Stone. It was then washed with Citadel Nuln Oil.
https://www.zinge.co.uk/collections/scenery-accessories/products/cinder-brickshttps://productsforwargamers.com/product-category/terrain/terrain-scatter-terrain/