As a national trade show consultant I have to say that word of mouth is a good way to find shows. However, another great resource for locating all things trade shows is tsnn.com. The website allows you to select an industry, location, and date, which will tell you of every applicable show worldwide. If you will be exhibiting for the first time it might be helpful to start with a smaller show in your area, then move to one of the large national shows (sometimes it can be overwhelming to start at one of the big shows). There is a lot of planning for a show, but if done correctly your booth can be both attractive and cost effective. I wish everyone the best! If you would like specific advice you can visit my website or contact me.
i can't really disagree with you that it is possible for trade show exhibiting to be a big waste of money...
That's why it's important to ATTEND a trade show first before you ever exhibit at one, and walk around and see what works and what doesn't work. Then you need to calculate how much it will cost to exhibit (which can be a lot) and make sure you have a plan to make money and not lose money, otherwise you should consider other marketing methods for sure!
Legs, if you haven't already checked, tsnn.com has a listing of almost every trade show in the US.