I heard you can trade shards for weather tms, if so where is that? and why isn't it listed on psypokes, nor lolstop?

I know I could breed the pokemon with a pokemon with sunny day but I would rather just teach them each with tms, because I finally have the right natures

OK, so:

On Route 212, the rainy area, to the right of the large pond with a long bridge (you'll know when you see tons of fishermen), and to the left of bog area, you can find a house. In there, you can trade TEN of a single type of shard for ONE TM machine. Shards are found in the underground, they won't take too long to find one.

10 Red Shards = 1 Sunny Day TM
10 Blue Shards = 1 Rain Dance TM
10 Yellow Shards = 1 Sandstorm TM
10 Green Shards = 1 Hail TM

I hope this helps.