So far as I know (I researched these because I wanted to replace some pieces) none of these are made any more, with the exception of the positive action latch on the top right (thery are made, but in antique brass with a brown-not white-catch). If you want an original article, you will have to start hunting. Otherwise, you can go for something that either approximates the look (like old bakelite knobs, for instance). You may have luck at antique shops that specialize in mid-century modern furniture.
FWIW, the little knob is found in only one place--a pull-out cutting board.