Crushing rocks down to sand is common. Here's the machinery.[1] The trick is to bang the rocks together. China seems to be making lots of sand for concrete. There are many manufacturers in China making rock crushers and sand-making machines.[2] China has plenty of mountain rock suitable for rock crushing.

Here's a marketing paper on making sand, and what to make for making concrete.[3]

[1] https://www.youtube.com/watch?v=1CpjRMICXNM [2] https://www.alibaba.com/showroom/vsi-crusher.html [3] http://www.metso.com/showroom/construction/new-type-of-crush...

Crushed concrete makes good concrete, but you'd still have to add sand.

Why not use riverbed sand and replace it with other sand?