I've listed this up on the .com forum, but figured I'd put it up here too as it is "$£$-ing me off. I had spent the majority of the campaign looking forward to using maxed out charge Takeda Great Guard
Anyway....
All the clans with the exception of the Takeda can recruit an additional "Great Guard" unit to the one they recieve, once they satisfy building, resource and Shogun-hood requirements. Following declaration of Shogun-hood, the Takeda receive a vanilla "Great Guard" unit in addition to the "Yari Cavalry", the ships etc. The Takeda Shoganate player is unable to recruit the additional "Great Guard" unit or indeed any "Takeda Great Guard" units.
If one looks in the STW2 encyclopedia, there are no building requirements for the "Takeda Great Guard", as opposed to the building requirements listed for the "Great Guard". Therefore the inability to recruit "Takeda Great Guard" is either a design choice, or a bug. I'm going with bug.