I buy mine locally at a place called Bachman's. If looking online, I would just find the best deal with free shipping
The directions will tell you how many tablets to use - yes, if a larger plant, more than one. Certainly buy the smallest quantity and make sure they work to your satisfaction. Just remember it won't keep the wascally wabbits from shearing things off now and then, but should keep them from eating the whole plant. I lost every single asiatic lily I had before I discovered these. Supposedly the bunnies may decide your garden doesn't taste that good and go somewhere else, but I can see this year that I still have a healthy crop of the varmints. They have eaten some hosta leaves (and I don't put Repellex under my hostas - too many of them) but have left my lilies and coneflowers alone.