I've never seen a clear case by Apple. I'd try a Spigen though...I've heard good things about them.
Their pricing is low too.
Apple are making one for the XR.

This is apparently it. It appeared on the press release for the XR in countries such as Canada, but not the US etc. and confirmed that a clear case was coming. But not on the store yet so who knows.
https://9to5mac.com/2018/10/12/iphone-xr-apple-clear-case/
And yeah, Spigen is on my list!