Two Suggestions, depending on how high your standards and budget are for this project.
First, contact a theatrical lighting supply dealer. There are a few candle choices out there. I have used the versions from Rosco and City Theatrical.
Rosco's flicker candles have 2 small lamps in a white plastic flame. They run on 9 volts DC and cost about $20 in the US. They are available as a tall candle with a battery connector or a short candle module with wiring pins. The flicker is not random so if you switch a couple of them on at the same time from a common power source, they will flicker in unison. In a dark room they are otherwise reasonably convincing, and reasonably cheap. If you are clever, you can work out a way to fit 3@123 batteries in the tall candle below the electronics. This will give you about 36 hours runtime.
City Theatrical's flicker candles were developed for Phantom of the Opera. They have 3 small lamps in a clear cast plastic flame, also run on 9 volts DC, have a true random flicker generator, and are much more convincing than the Rosco candles. They are also at least twice as expensive. They are available in 2 sizes of candles and as a module with the flame connected to the PC board with about 6" of wires so you can build it into a candle or lantern. There is a dimmable version available. I usually use the modules and build them (and a battery pack) into candles or lanterns as needed by a specific play. If you started with a host like a ships lantern, there's no reason you couldn't make something fairly weather-tight
At a trade show about 2 years ago I saw a module that used a blue/yellow bicolor LED with a blob of hot glue on it as a flame. I'm not sure who makes it, but I've seen it in a lighting supply catalog or 2. It was interesting, and about $40, but I didn't get one. I think City Theatrical's version for the same money is more convincing
Second, do a web search
There are a couple companies that have recently come out with very convincing candles using LEDs as the lamps, but all I've seen so far have been mains powered. And they were more than $40 each candle.
On a more thrifty note, my GF bought a candle out of a catalog last Christmas. The type of thing one might put in a window at holiday time. It uses a yellow led encased in a plastic flame as the lamp, runs on AA batteries that go in the plastic base/candleholder and was proudly made by "made in China". It is not quite as convincing as a Rosco candle, but it cost less than $10 before shipping.
