What got us started was having a few on our demo songs used in the movie "Radioactive Dreams". The director Albert Pun really liked our stuff. Then he gave us the chance to right some score for it. That scene was where a garage door opened and the two guys inside were able to breakout into the post atomic war future. I sampled a circular saw on my Casio keyboard and played it back in different pitches. Seemed to work well!
Bottom line for me was to know somebody and be willing to work for almost nothing until they get to know you. For my partner Tony and I, we did a lot of B grade films back in the '80's. You need to have a very good portfolio and have to pound on doors. Nobody will know who you are unless you make all the first, second, and third moves.
Good luck with this. I loved the work.