While this may not yield the exact same functionality as 'findpeaks', a new function introduced in R2017b 'islocalmax' should have similar functionality.
If you take a look at the example below, I have provided some code below that is identical to the first part of the example using 'islocalmax':
year = sunspot(:,1);
avSpots = sunspot(:,2);
m = islocalmax(avSpots);
plot(year(m), avSpots(m), '*');
'islocalmax' does not have the exact functionality as 'findpeaks' but should suffice in some use cases.