The best resource I’ve found for tenkara-related courses is Discover Tenkara. They specialize in taking tenkara information and techniques Japan (the birthplace of tenkara) and bringing it to a wider audience outside of Japan. Their courses are primarily video-based, but they include lots of other supplemental information in various formats.
If you’re starting out, I recommend the Manipulations Volume 1 course for $49.99. Way cheaper than going to Japan yourself or hiring a guide to explain stuff to you—and that’s assuming your average guide would know to teach this stuff in the first place, which is doubtful.
Here is a link to all of the rest of their courses for you to check out. They range in price from $20 to $97 each.
If you want to save money and buy ALL of the Discover Tenkara courses at once, sign up for Discover Tenkara Full Access. It’s $297 (normally $336.93 if you were to buy them all individually). But use the coupon code THF10 to get 10% off of that $297 price, bringing the total down to $267.30.
I’m an affiliate for these courses. If you buy the courses through these links, I get a commission. That said, it’s not in my best interest to recommend bad products, even if I make money from them. It’s way more valuable to me in the long run for people to trust me and my opinion on tenkara stuff rather than to make a few bucks from courses.