It is quite common to see some completely different devices using the same frequencies because the manfucaturer didn't really have much of a choice. This directly limits the frequencies that any particular product can use.

You might look for some wireless devices that use similiar frequencies but have different channels. I doubt you'll find remote control vehicles that use different channels, but you might. They'd probably cost more though because they'd need more electronics inside to let you select which channel each one was on.

but nitro fueled RC vehicles can be used without a permit
but only on private grounds/property and with owner of the land permission ,which is fair enough because some nitro fuelled RC vehicles go extremely fast,and would cause a nasty injury if it hit somebodys foot/leg on the main street,if that helps at all?

ps:and of course there is the high level of
noise pollution to be taken into
consideration too,so all in all !
and i have never been to sunny california in my life,i will stick my neck out and say no you cannot use a gas/nitro rc vehicle on pavements and streets purely because it
makes sense not to

http://www.nitrorcx.com/?gclid=CIeHrqnN9Z0CFYJx5Qod0Qz1ow
http://www.hobbytron.com/NitroRCCars.html
http://www.rctoyhouse.com/

and ebay.

Dont forget to buy fuel