uController SPI Over optoisolator
There are digital isolators from different companies to support your application, but here I feel an important thing OP is missing, what is Insulation Rating(kVrms) you are looking for. 

Based on the insulation rating Analog Devices link offers you several SPI isolators.

Not only Analog devices, you can find digital isolator from Linear Technology .

TI doesn't have dedicated link for SPI isolators, but the app note on page #5, they explain how to use their digital isolator for SPI. 

Even you can look in to MAXIM link also for their digital isolator supporting SPI application.

There are some more options like IL717 from NVE isolations, link here which talks about using NVE isolators.

Even you can look into Silabs, for isolation products, but I am not sure whether they have something dedicated for SPI.

Now, the onus is on you decide which isolator you want go with, based on the availability of the product in your region and Insulation Rating and most important factor is the price if you are going for mass production.

Hope this helps you to understand the SPI isolator selection in future as well.