One good way to start obtaining quality backlinks is to look for blogs or online magazines related to your niche and guest blog for them. Of course, you should be ensuring that your guest posts contain relevant and useful information, not just another method to promote your product, otherwise Google may just treat such backlinks as link-farming.
This article on guest blogging might be of interest to you: http://searchenginewatch.com/article/2194396/How-Guest-Posting-Propelled-One-Site-From-0-to-100000-Customers
Another method which can potentially be explored is the idea of "collaborating" with other ecommerce stores that are related to yours. For example, since you are selling equestrian products, you can collaborate with stores that are selling health products for equestrian riders (not sure if there's such a thing, but it's just an example). You can have a mini-entry below your product pages that goes "Looking for health products to go with your training? Check out Shop B to complete your equestrian experience."
Likewise, if Shop B writes the same about your shop, you would be able to receive a backlink from their store. Better still, consumers coming through that backlink will likely fall within your target audience. This becomes a win-win for both stores.
Hope that helps!