You’re right, there aren’t that many poison Clips, but there are quite a few, not as many as some other methods, but you can have fun with the ones that are there.
If you’re looking for poisoning you can use the website filter, in “Method” just click on “Poison”,
There are several Clips featuring poisoning and some other method (strangling, stabbing, shooting),
But if what you are looking is for a Poison only clip, there are even more seldom, but there are some.
Here is an example of a Poison only Clip hehehe
http://www.bestdeaths.com/store/i-mean-it-young-runner-poisoned-1302.html