Contact local theaters or drama groups and get in touch with their technical directors. Tell them you're interested in props work. Expect to do some free work for community theaters in order to build your resume before working for professional theaters.Theater props is one of the easier roles to break into in the world of theater. This type of work tends to appeal to a very unique type of artist, so there tends to be less competition and skilled props artisans are highly sought after.
Obtain as many ready-to-use props as you can. The director will give you a props list. Don't think this means that you don't have to read the play's script--read the props list, then read the play in order to see how the props are used within it. This will affect many of the decisions you will make about your selection. For the same reason, watch rehearsals in order to see how the actors will be interacting with the objects and what special considerations need to be made.Before you obtain anything, talk to the director about the props list. Ask any questions you may have and go over each item and make sure the two of you are on the same page regarding what is wanted and what you have in mind. Believe me, you don't want to find yourself in the position of having to replace many items later because the director finds them unacceptable.If the theater you're working for has a store of props, this is the first place to go for what you need. If not, it's usually acceptable to call on the cast and crew to see what items they can volunteer. Be sure to make it clear to anyone who loans props to a production that there's always a risk of loss or breakage--theater is rough and tumble!
Build or purchase whatever is left on your list. You can buy some items at the local department store, but it's better to avoid getting too much new stuff this way because it will be too recognizable. It's better to shop at thrift stores and garage sales, which are great places to find some of the older and more unique items. The most fun props, of course, are the ones you can't buy. Specialty props are unique novelty items or fake, special effects objects that must be built by a skilled artisan. This author has had to build items such as fake dead rabbits, magazines with fictional titles, glasses filled with solid, fake drinks that won't spill, and fake amputated toes.