Tile grout

Gallows Bay Ace Hardware.

There are also a couple tile places near the refinery, one by the car parts shops and another (I think it's called Flooring Specialists) next to Tropical Plumbing east of the refinery.

On the west end, Kama Kris sells some grout as well.

If you only need a basic white or tan, some of the other small hardware stores like Princesse Hardware may also be able to help you out.

If you can’t find something locally, I order off of eBay frequently for things like this.  Usually because I’m trying to match a special color that isn’t available locally any longer.  Just be sure you are purchasing from an established seller with good reviews.  The sellers there are competitive so they tend to ship fast so they can get good reviews.  

Thanks for the input. Much appreciated.