Mail a simple mailing first class and see if you get any results. From my experience, a simple black and white mailing is almost as effective as a costly full color mailing when selling wholesale. Don't be too disappointed if you only get 2 or 3 phone calls from a mailing of 100 pieces. It is worth trying, but direct mail is hard to make a profit on. Trade shows are a way to talk to a lot of stores in only a few days.
Shows can be expensive.
Trade magazine advertising is the cheapest way to reach a lot of stores. They are not available to the retail consumer. There are trade magazines for shoe stores, book stores, etc. The Needlework Retailer is the best place to advertise to reach needlework stores. While running an ad in a trade magazine is not cheap, on the basis of cost per store reached, trade magazine advertising is very inexpensive.