Repco, Burson and most other auto parts shops will be able to order them in, they aren't likely to have them in stock. I purchased my last set from Repco, they were around $20 each, so a bit cheaper than getting them from the dealer.

The OEM specified NGKs work roughly the same as a plain copper plug, the iridium electrode is just much more durable. This allows the 100,000km service interval that is often specified. If you buy the plugs from Honda they will be the same as the ones you would get from elsewhere, they will just come in a nice Honda box/bag maybe.