Its not a good idea to flood the engine on this car (its a high performance Nissan design), you'll invite more problems.
As for parts try these guys:
http://www.infinitipartsusa.com/
OEM Nissan parts not autozone knock offs at a fair price.
Use only Nissan OEM sparkplugs, anything else and you WILL have problems gauranteed.
Your car is an Infiniti and not a Chevrolet. The reality is you'll have to "pay to play".