You can buy the battery operated candles at Bed,Bath & Beyond, A.C. Moore's, Michael's, Plow & Hearth and they are wonderful. That is all we use anymore in our house. We live in a Sr. Citizens community and about 3 yrs. ago there was a bad fire in a garden apt. one windy Jan. night started by a plastic coffee maker being put on a burner that was on by mistake. A man lost his death because he went back into his first floor apt. to get some important papers and the ceiling from the apt. on fire fell on him and killed him. They had to tear the entire building down and rebuild it. Every since then, we only use the battery operated ones. They have some that are scented and the outside feels like real wax. They have a lot of hours of use, something like 100 or 500 before you have to replace the batteries. They are LED lights. Candles that come in lots of colors plus white and off white.

You can make nearly any 120V light into a 12V light. There are adapters to convert to the type of socket for 12V available and there are 12V versions of standard looking A lamps. Those are the most confusing however because people will replace them with a normal A lamp and wonder why it barely glows. I know nothing of this vendor. It was just the first thing that googled up to show you an example. Here is a link that might be useful: socket adapter

I've replaced some of my low-voltage landscape lights with high-output CREE LEDs. A 3 CREE LED bulb uses about 3.5 watts but puts out the equivalent of a 25-30watt Halogen. So just get a low-voltage floodlight landscape fixture that uses a MR16 Halogen and swap out the bulb with a MR16 CREE LED. The bulbs cost about $25 on Ebay. I got mine from a seller named iggybabie and they've worked perfected outside everynight for the past 18 months...they are plenty bright for reading purposes.

If you can get your hands on a router, you may be able to route a channel or dado for the wire and then glue in a spline to cover it. This works fairly well for a period of time--a few years anyway--but sooner or later the spline is likely to need maintenance or replacement in a weather-exposed environment. It's not a perfect solution, but it's the best I can think of from an aesthetic point of view. Small diameter conduit is another option. It's less attractive but probably longer lasting and lower in maintenance.