Yup, XA4 is hard to find but the only model with the 28mm lens.
I have XA and XA2. I think the XA2 is better value for money... about 1/2 the price of the XA. And yeah, the XA is not necessarily easy to focus. With the XA2, there are only 4 settings... so its more like a set-and-shoot sort of camera.
When I use these cameras I want to be able to be more spontaneous... and the XA2 allows me to do that, whereas i find the XA makes me approach it like a regular RF camera... in which case I might as well just my Bessa-R.