aren't they just a normal fairly boring bolt ?
That depends on what is missing from the jack in question as rob said
i have lost the pins which hold the handle on
Looking at my badly annotated and out of focus picture below (and ignoring the custom floor covering of tasteless pink carpet and Katy fur) I am assuming the Bolt "A" is missing, <comment edited for reasons given in next post>.
The problem would come if the Pitman Pin "B" has also gone walkabout, and to get the corrct item would probably involve speaking to Arbil or Hi-Lift direct.
Bolt "C" is described by Hi-Lift as a "Safety Shear Pin" and so should only be replaced with the correct part, but this does come in the jack overhul kit (that's why it's shiny at the moment)