My playgroup doesn't really use attribute damage. I'm looking for some way to replace my viper's poison.
Old school d&d used to use HP damage and conditions like paralysis for poison effects. They got rid of them in 3.0 however as they felt the effect was too dangerous and could end a fight too quickly, especially if the PC's were on the receiving end of such. You might want to look there for ideas. There are also any number of good 3rd party products written in recent years about poisons.
The reason question is what would you like the poison to do? Not all poisons will kill (at least not right away) and can be used to add a lot of very cool effects. Sounds like you need to speak with you DM about what he or she is comfortable with.
Also rangers and alchemist are typically your best resources of poisons.
Rangers?
How about a saving throw on the charcater’s turn to avoid a condition. It lasts until succeeding.
Certainly rangers, ever heard of "milking" a snake? I think the new ultimate wilderness has some sorta rules for this although honestly I've not read it yet even though it is sitting on my desk.