They are common enough that they can be ordered through CZ reps, but, there is a significant wait time. CZ mothereship has been overloaded with Euro defence contract work in the last year and a half which takes priority for them. I ordered a .17 HMR barrel last year in November and it didn't arrive until June. The worst part is the stringing along...being told that its coming in a few weeks at least a dozen times.
Lildja does make a nice barrel upgrade for the 455 out of stainless. Costs 3 times as much as a stock CZ barrel but they are excellent shooters, modified match chambers, bored and lapped out to be lest invasive on sizing the bullet. There are probably importers here in Canada for these.