Seems plausible, but it's very odd to me that a place like San Marcos Growers has never stocked those, if they do well in CA.

Also, though white ones exist, the colored forms are far more common in the trade. I feel like one of our old Norcal people would get this right away, but they all seem to be gone these days. [sad emoji]

Why not an Oleander?

Doesn't look right for oleander to me.

Nor me. Leaves are not long and narrow. Blooms wrong shape.

Ok. Here's an off the wall suggestion. Phlox paniculata.

Arizona dwarf Oleander

Occam’s Razor