Interesting comment about the UWAN 28mm curvature, I haven't noticed it in a f4.9 Newt but then again I understand sensitivity to it varies significantly among observers and also depends on the curvature inherent in the scope.
Easiest place for the OP to get Pentaxes is probably:
http://www.telescopes-astronomy.com.au/
who are in SA. Unfortunately that site is among the worst laid out and most difficult to traverse that I have ever encountered, it was only completely by accident that I stumbled across his Pentax pricelist and I had to bookmark it to make sure I could find it again:
http://www.telescopes-astronomy.com....-pricelist.htm