I am very interested in the Chinese Dadao and how they were used in combat. Is there any good resources out there on the use of and training with the Dadao specifically? I've seen a lot on the use of other Chinese swords but none on this one. Thank you for any help you can provide.
There's been some pretty good scholarship and interest in the Dadao recently. There's a few forms or methods which have managed to be incorporated/carried along with various forms of kung fu - here's some demonstrations from a Mantis kung fu school. Others are attempting to reconstruct Dadao movements from old military manuals.
It's a bit difficult to say how useful those are, given that the Dadao became the most widespread at a time when rifles were the standard weapon and the fact that many of the "Dadao militias" or "armies" were extremely variable in training - sets and manuals might be anywhere from very practical to utterly useless, and it's hard to say.
There are two kind of weapons that are sometimes referred to as the Dadao...
There's the short Dao (can still be wielded with one hand) and then there's the Dao attached to a long pole.
In combat, the first version of shorter Dadao is used mainly in melee against other armed/armored fighters. The Dadao let's your cut Spears and Staff and its weight give you an advantage over the lighter Jian against armored opponents. Dadao is devastating in close combat against most weapon simply because its curved blade is ideal for slicing in close quarter situations.
The second version of Dadao, which is used by the famous Guan Yu in Romance of 3 Kingdoms novel (and the historic figure as well). This Dadao has great range and power. You can literally chop the legs of a warhorse with it. Hence its use as counter against a cavalry charge. It has advantages over a similar weapon, the traditional Chinese spear in that it is much heavier and capable of cutting as opposed to just piercing.
Various traditional Chinese Wushu includes Dadao training (but mostly the first shorter type). The longer Dadao is more of a military weapon than a civilian one, but there are still Wushu schools that will teach it.