I think the shut off valve is typically installed inside the firebox. This is normal.If you decide to get gas logs, the dealer should visit your home, take measurements, and make sure the gas outlet is located where it can be easily connected to the gas logs. For example, if the gas pipe is in the left side of the firebox (it usually is), you want to make sure the gas logs unit has a connection on the left for the gas. These are technical details you should let your installer worry about.

If you are concerned about having a hard time putting your hand inside the firebox to regulate the gas logs, this is almost never an issue. Most systems come with remote control devices, so they turn on and off just like your tv.