This advice might seem a little late, I joined Style Forum some months back but have not been as active since I handle trade shows and events for a living. One way is to find a good venue that caters to designers and retailers.
There are plenty of good shows where you can buy a booth spot and you will get lots of visitors (designers & retailer reps), you will have to ferret out the good leads from the bad. I also would suggest throwing your own event, I have done several in the past. My shows are mostly for tailors who sell bespoke tailoring and are looking to grow their client list.
I have some pics from my last show, but I do a good number and I handpick 20 to 30 guests, through HTML email and marketing ( I have a list of potential buyers (not retail, men's bespoke clothing) that I developed on my CRM, over several years).
I normally contract art studios, food and beverage providers and I include valet parking for my guests. My cost is not as extravagant as it sounds, a good night will cost me $1000.00 in services and the tailors can usually generate around 10K before the night is over.
My business model is different but if you create a good event and market to the right schools and look at the appropriate places like: The Business of Fashion, you might be able to build a good database and design a venue that will attract the designers you would like to partner with. I hope it helps and maybe you have already implemented a similar strategy.