Here are some that come to mind...

Leymus 'Blue Dune', although not clumping it is a true blue

Festuca 'Elijah Blue', 'Boulder Blue', 'Superba' These are low growing, clumping grasses that work well as edgers, borders or groundcovers

I love blue oat grass, so you might want to consider looking into this one too. The festucas are nice, but I like the blue oat better. It may be taller than what you want, but it's very
slow growing, at least for me.

Here is a link that might be useful: blue oat grass