I'm about halfway between Springfield and Branson. You want Busiek State Forest. Our property backs up to it. The Downhill bike shop in Branson can direct you there. Or you can find all about it on the 'net. Or you can PM me and I'll have the MTB riding son in the family fill you in on what he knows about it. He's also been over to the Chadwick area, but was not impressed with it as it is more geared to the ATV and motorcycle trail riding crowd. There are also some pretty popular MTB trails north of Springfield, but from what I hear, they all get in line behind Busiek.
It's all downhill from here. Except the parts that are uphill.