Break Free CLP is just about everywhere. Walmart carries it. About every place that sells firearms will have it.
There are fancier lubes, but Break Free is still one of the best rust preventatives available, and it's a good lubricant.
The Military has been using it for 20 years or so, and it's still in use today, so it has quite a track record.
It's not expensive either, and available in liquid and aerosol.