It's probably that it's two in the morning, but for the life of me I cannot find light ladders in my Vectorworks resource browser. I have Vectorworks '11 and I'm just looking for some 3 rung ladders.
Yeah, the default Vectorworks libraries really aren't very useful, and some of the symbols are just horrendous - most people I know have come up with their own libraries through a combination of making their own and sharing with others. It's probably best to just draw it to whatever size yours are and save it as a symbol for future use - may also want to create a top view/side view symbol to use it in a ground plan/section, while you're at it.