I think the CZ polymer mags are just as good as the steel mags, it just comes down to preference. I like steel, myself. i will agree that Cz 452 magazines are a little on the pricy side at around $30+/-. They are nice quality magazines, so at least you know your not buying cheap junk accessories.
Anyway, the factory parts i switched out for steel replacements are:
-polymer magazine well
-plastic magazine floorplates
The accessories i bought because of the quality:
-steel Single Shot Adapter (awesome, and a must have)
-CZ kozap rings (had to shim a little for 3/8" groove)
All parts (except the kozap rings) are old new stock Brno parts and were obtained from a gentleman i met on another forum (RFC). He goes by "Brnomann" on that site, but also sells on GB under the name "zdeno". great guy to deal with.
If you are looking for something in particular that is CZ or Brno related, email him from the GB site and ask.
DW
p.s. I also replaced the factory action screws with torx head screws from Rimfire Technologies:
http://www.rimfiretechnologies.com/ ...they are very nice and match the bluing perfectly.
another option for action screws is J&P:
http://www.jnpgunsprings.com/ , these are more of a matte finish