Anything beyond the Beginner shamisen, is likely best to have custom-made for you. This process requires a reasonable amount of knowledge on not only the Tsugaru Shamisen itself, but also your own personal preferences and needs based on your use-case and experience.
At this level, you are likely well-versed and experience in shamisen already.
Custom made shamisen
Pros:
Best possible sound and overall longevity
Can last an entire lifetime with proper care (or even be passed down)
Can be customized to one's own playing style and preferences
Cons:
Requires quite a bit of knowledge of the shamisen to purchase
Requires more constant care to maintain over the long-term