In summary

The obvious place:

1. Case study library of the Service Design Network

On local government websites:

1. British Columbia

On agency websites:

1. Livework

2. Engine

3. TPX Impact

My two cents

Service Design Network

Obviously one of the first resources is the Service Design Network website that has a case study library. The little trick is to use the filter function and then only display the case studies that come from the government category.

British Columbia

The British Columbia website has also a few case studies about Service Design. For example, you'll find one about Service Design and autism services.

Then it's also pretty smart to have a look at the big agency websites.

Livework

Livework has a few case studies about Service Design in the public sector. For example, one for Public Health England, another one for Transport for London, or another one for the city of Amsterdam.

Engine

Engine has also a few case studies mostly about the London Borough of Southwark.