Martin,

I'm going to give you the benefit of the doubt that you are not a troll and give you an honest answer. There are NO vegetable oil based lubricants that are practical and effective for bicycle chain lubrication. The useful lubricants on the market are petroleum based or synthetic. The only possible vegetable based lubricant I can see being at all useful MIGHT be to replace paraffin with carnuba in a hot wax type lubrication. I'm assuming this has been tried and, since it hasn't gained popularity, probably didn't work well. While some people swear by hot paraffin applications, IMHO they are far more trouble than they are worth with marginal, if any, advantages over a liquid solvent suspended wax lubricant.

Keep your chain reasonably clean (good advice in some above posts) and lubricate it whenever it gets noisy. Avoid over-lubrication and wipe away excess on a regular basis.