The simplest way is word-of-mouth referrals. Chances are that a current customer runs with people who are a lot like them and appreciate similar things. A way for you to “clone” your best customers — because they order a lot or they’re just easy to do business with — is to have them introduce you to people who you’ve not yet done business with. This can be done by referral or a testimonial letter.
Alternative to a testimonial, you can ask them if they would be willing to talk to a prospect that you’re pursuing. Being introduced by a third party is just as strong as being given their name and then approaching them saying, “So-and-so is a customer of mine, and he suggested I contact you…” A business may screen calls, so if they can be introduced by a third party (i.e. a current customer who is satisfied), then that cuts through any type of barrier there is between a company and a target prospect.