From: Jeff Walther 
  In fact, I have not been able to find precoated board
(photoresist
 coated) in the .050" thickness.  So I will either need to use a
 liquid photoresist or try a toner transfer system. 
Personally, I would avoid liquid photoresist and use dry film in its
place. You could contact Fred at Far Circuits
(
http://www.farcircuits.net/) as he will supply boards precoated with
dry film photoresist. URL for supplies is
http://www.farcircuits.net/supplies.htm. According to the site, he will
supply 0.047 material laminated with Dupont PM115 photo resist film.