It depends on which one you are wanting to go to, but here are all of them:
The store for horse items (food, saddles, bridles, etc.) is under the breeding tab of "breeding" and says "The Shop"
The second shop is for items you buy with passes is also under "breeding" and says "The Black Market"
Then there are the shops for your equestrian center
the shop for the basics (meadows, boxes, seeds, etc) says "the Shop" BUT is under equestrian center tab.
The last shop on Howrse for items (better pets, boxes, etc) is called "the secret market" under equestrian center tab.
Those are the shops for items but if you were referring to where to get horses go under trade and there are auctions and private sales, that is where you buy and sell horses.
Breeder ---> The Shop.
You can't get one.
they sell it in the secret store
Boreas' lunges are for sale in the normal Howrse store (for your breeding farm) for the price of 9 diamonds. View the Related Links section to see where you can find the Lunge in the store.
Breeding → Store → Exchange Items. It is a square button under the description of the store.
Buy it in the EC store.
You can complete objective 26 on howrse by selling stuff at the store, entering your horse in competitions, and selling horses.
you go to the store and you go to companions and then you chose the one you want
You have to buy saddlery from the store under the 'breeding farm' page.
Go to Breeding >> Store >> Equipment and buy a saddle!
go to the store and click on the thing you want, then select how many.
There have been no cards for Howrse since 2009.