What is your goal with this bridle?
Do you just want a prototype for your horse? In that case I would find a local leather worker, do a mock up in nylon, ride in it for a while, and then decide if it works well enough to make a final version in leather.
Do you have ideas about creating and marketing it as a product? In that case you really do need to patent it, and to have the start up costs saved. I watch Shark Tank and Dragon’s Den and there are always people who have sunk a hundred thousand dollars into a prototype of some gadget that no one wants to buy :). If you do want to market it,you have to think through in advance (1) does your target market see a need for this item and (2) can you manufacture it for a cost that allows you to sell it at a price point that covers your expenses, makes some profit, and that people will be willing to buy it at? Then, how are you going to market it, and how are you going to compete with the similar but different items already out there?
The horse market is limited, and is divided between western and english riders. The per cent of these riders who want a very different design bridle that may not be legal in showing in their disciplines is fairly low. Some of them have Micklems, some have the high end brand “comfort bridles,” some have side pulls or cross under bitless. Etc.
You can’t approach a vendor unless you have a product you can deliver at a wholesale cost that you can make a profit on and that they can then make a profit selling retail. I am not sure of the markup in horse products, but let’s say it costs you $50 in materials and labor to make a bridle. What do you factor in as costs for marketing? What amount of profit do you want to get back from your investment? Maybe you sell the bridle to the vendor for $100. Then they sell it to the customer for $150. Is your bridle desirable enough that someone will pay $150 plus sales tax? How will you make it desirable? How much advertising do you need to do? Maybe you sell the bridle to the vendor for double what it cost to make, and you still don’t have enough money to do the advertising you need to do. These days that absolutely requires a good website, as well as print ads on on line ads in selected venues.
In other words, you can’t just expect to approach a tack shop with a sketch, and have them say yes and give you money to get started.
If you feel that you don’t even have the cash to patent your idea, I would say you are not in a financial position to launch a new product.
But you could certainly have a local leather worker build you a prototype, ride in it and see if it works, and enjoy it, not worrying if anyone copies it. Chances are they won’t.