There is only one official case from Google for the Pixel 3a/3a XL. And that is the Pixel 3a/3a XL Fabric Case .
It is officially available in Singapore via Google Online Store (Singapore)  and it retails for S$60 for either Pixel 3a Fabric Case or Pixel 3a XL Fabric Case.
Three colors are available, Carbon, Fog, and Seascape. For my Pixel 3a review unit, Google sent me the Fog, as shown in the pictures below.
For the interior of the case, it is wrapped with soft microfibre lining for scratch protection.
The case is made from polycarbonate, and the outer layer is wrapped with polyester and polyamide fabric.
As an aesthetic design, Google chooses to make the power button of the case to be the same color as the microfibre lining. In this case, it is orange.
The color also matches the power button on the Pixel 3a/3a XL itself.
For the volume button, it is embossed in the case. When I first started using the Pixel 3a XL with the case, it took me a while to find the volumn button based on feel as visually it looks the same as the case.