Original M42-PK now available from B&H.

Funny coincidence! The best price I used to find was factory direct at the Pentax Webstore-- $35 IIRC. They're no longer listed on the Pentax Webstore.

--
How poor are they that have not patience!
What wound did ever heal but by degrees?
Thou know'st we work by wit, and not by witchcraft;
And wit depends on dilatory time.
Othello (II, iii, 376–379)