Check out Yongnuo on ebay. Good products. I have two wired units. One is the simple pushbutton. The other is like the Canon TC-series. Interval timer, long exposure timer etc. They also have wireless but I haven't tried those. Pick the ones for the Pentax series.
YONGNUO TC-C1 Timer Remote Cord
Compatible to :
CANON 450D/400D/350D/300D,PENTAX K20D/K200D/K10D/K100D,GX-20/GX-10