Maybe try some fishin' for Embroidery business.
You've got two customers, the ones you have and the ones you don't.
For the ones you have (or have used your business in the past), send them something.
Take their company name and redesign it or move it around their logo. If they used a stock design before, find something similiar but with a new twist.
It's probably standard but, when ordering for any customer, always order a few extra.
This way, you'll know what garment they prefer. Later on down the road, for example, when their hats or shirts are showing signs of aging, you send them a new one.
Of course this one will look new and different from the original, which may be enough to get the ball rolling.
The customers you don't have, well, this may be easier, especially for new start up companies which aren't advertising (or wearing promotional products).
You've seen from your existing customers what works and what doesn't.
Therefore, use your imagination. Use a stock design or use some creative editing and then, send them somthing.
It doesn't matter who it is, people enjoy getting something for nothing.
They will look at you differently. You didn't have to do this but you did.
It shows you are taking an interest in promoting their business (while promoting your own of course). They will spread the news of their good fortune (Hey, this guy is giving stuff away!!!)
Make sure to include a price list (a profitable one) and a couple of business cards with your free sample.
Good luck fishin'
Tim