Yes, Pentax USA sells the adapters on its web site.  They cost $30, a
little more than the non-genuine items usually sold on eBay, that can
cause problems.

Go to:
http://www.pentaximaging.com/index.jsp
and click on the link "Purchase Our Products".  Then click on "Shop
Online".

In the left sidebar, under the heading "SLR Accessories", click on the
link to "Teleconverters/Mount adapters".  Finally, select "Mount
Adapter B".

Adapters are also available from Pentax authorised dealers.

Yes, Pentax makes one for use on their K-mount line of cameras:
http://www.adorama.com/PXAB.html

Adorama also sells several adapters to mount Pentax screw mount lenses to
various cameras, including Pentax K-mount, Minolta Maxxum, Nikon, and Canon EOS.
Go to Adorama.com and click on 'Cameras & Lenses' in the menu at the left of the
screen. Then on the next screen, under 'Lenses & Accessories' click on 'Lens
Accessories'. Finally, on the resulting screen under 'Refine Search' click on
'Adorama' under 'Manufacturer' and 'Lens to Camera Adapters' under 'Type' and
then click on the 'Search' button.

'Adapted' screw mount Pentax lenses won't work with some DSLRs, but they do work
with 'function limited' on Pentax DSLRs.

See this web site: <http://www.cs.tut.fi/~jkorpela/usenet/xpost.html>