You can do it yourself. It's time consuming, but still possible and easy.
Valve lapping compound is available at most any autoparts store (gritty paste). Use some paste on the valve sealing surface and turn the stems (after removing the springs and stuff) while applying light pressure. Small suction cup tools make it a litle easier on your fingers and thumbs, but once done, you'll have smooth mating surfaces that fit nicely.
Jay