Kerstin here from the Shopify Guru Team :)
One way of sourcing branded and specialist products would be to contact the manufacturer directly who will then be able to provide you with a list of legitimate wholesale suppliers. Attending a trade show would also be a good way of getting the right contacts. We have a guide called Finding and Working With Suppliers that might interest you and there is a supplier directory towards the bottom that you can check out too.
All the best,