Pentax Canada lists the same screens as the K7 used
so any screen out there for a K7 should work
A lot of people here here buy the jinfinance ones (they are a great price
the Katzeye's are the most expensive, but also the brightest and allow full customization of grid-lines adding britescreen etc
in between you have companies like the one below where i just ordered one, i went this route as they had a good selection of reworked screens to choose from (from ones not really any different than the jinfinance ones though pricier) to ones that are much better screens but not customizable like Katzeye and i haven't heard anything bad about them. There really should be a sticky on this topic
Focusing Screen