It seems the budget Google Pixel 3a and 3a XL phones have something in common with their flagship equivalents besides the brand name — they're being leaked a lot. Just today, Google added both phones to the Play Developer Console, and now the 3a has made an appearance on the company's online store.
Once you click the 'Phone' drop-down menu on store.google.com, a new link to the Pixel 3a is listed. There's also new 'Google Pixel 3a Case' and 'Compare phones' links. The case link goes to a page called '"pixel_3a_case_fabric," so it's probably safe to assume Google's signature fabric cases will be made available for the devices.
All three links are currently non-functional, but Google adding them to the main list could mean a launch is imminent.