Bluecorn Naturals sells pure beeswax candles. Their tapers (the normal thin candles) burn 1 hr per inch. So a single 10'' taper candle gives you a 10 hr burn time. Bluecorn Naturals also sell their products on Amazon and they are 'prime-able'
Their pillars (the big cylindrical candles, which I'm not sure are medieval) have insane burn times. Their largest pillar burns for 240 hrs.
Pure beeswax candles also smell like honey while they burn
I'm going to pick up some tapers and a lantern or two for DoK this year.
If anyone's interested, real medieval candles were either beeswax, tallow, or a combination of the two. Beeswax is self explanatory, tallow is rendered from animal fats (think medieval crisco) and a hardener is added so it just doesn't melt away (it's very soft). Pure beeswax, think upper class and the church, then start to add tallow as you climb down the social ladder. The poor would make their own candles from pure tallow they made from suet (leftover fat basically) from their food. Tallow candles will basically smell like you're frying a hamburger when it burns, whereas beeswax gives off a nice honey scent.