Some of the more expensive Canon and Nikon models have built in blinds. Would be a nice addition to the K-1 given it's 'field camera' designation. Even an external finder cup with blinds would be a welcome addition for those that do long exposure photography. A piece of gaffer tape will work as will a bit of dark cloth.
I built a cover that works and there are directions in this thread:
K-3 underexposes with ND filter - Page 2 - PentaxForums.com
And a lot of info in this thread:
Viewfinder blind - PentaxForums.com