Well, I learn something new every day still. As much as people rave about Animal Plastics products I would have expected higher build quality/better manufacturing processes.
Most pet stores carry aquarium grade silicone and would be both the easiest and most expensive place to find what you need.
However, After a bit of digging I turned up a 3 pack of aquarium grade (100% silicone with no mould/mildew inhibitors) at the local hardware store for around $12. It was Weathershield brand and specifies that it is aquarium grade on each tube.