Trade shows near Davis:
Check with chambers of commerce in Davis, Sacramento, Oakland, Livermore, and San Francisco (and other nearby locales). Contact the events managers at civic centers near there. Scan trade magazines (Aviation Week & Space Technology has a page of trade shows listed nearly every issue). Do an internet search (The California Job Journal has a Career Fair on 10 June at the Sacramento Convention Center, open to the public). Check the business sections of the local newspapers. Email the business editors of local papers. Look in the Yellow Pages under Trade Shows and call whoever is listed. Call local charities, ask if they are involved in any trade shows nearby, and ask if there is anything you can do to help (that will gain you admittance, and a badge). If you find a show, call the director and offer to do a show at a reception, and you would be willing to accept a discounted fee in order to market yourself (discounted here means marking up your normal fee to a Trade Show fee, and then discounting it back to your normal fee). Check with your local colleges/universities -- they market themselves at technical symposiums all the time. Your profile says you are a student -- if at college, go to your school's marketing/ publicity office and offer to volunteer.
As far as getting into a "closed" show, closed is a relative term. Some are only open to people in the business at hand, some have tickets, some have relatively cheap/simple registration, some are open to the general public for free. If it is limited to a particular segment of business, get creative. Bluff your way in. Go on the afternoon of the last day, after exhibitors are starting to close their booths. Call the event manager and ask for a pass (it's amazing what people will give when you ask for it, and it doesn't really cost them anything). Find a publication that needs an article written about the show, offer to do it for free, and get free media credentials. Find someone who doesn't need their pass/badge (they are going home early, or have thrown it away) and use it. Tell the person watching the door that you were in the building for other business, and saw what was going on, and ask if you could just go in and look around.
Read Eddie Tullock's book.
See: SAN FRANCISCO TRADE SHOWS
for info on 87 upcoming events there -- many have links to a contact person, and they also list venues, including hosting hotels, etc, which you could also follow up with.
As close as you live to the population centers of the Bay and the state capitol, you should be in and out of two or three shows by the end of next week.
Face it, if you can't sell your way into a trade show, you shouldn't expect to be selling products as a trade show magician. Strong convincing skills and persuasiveness would be required in both cases.