Here's a chart that will give you an idea of how yarn weights are classified.
If you are making a project that requires 13sts=4" that just means that your knitted piece will have 13 stitches in every 4" across a row of knitting. This is a pretty chunky knit.
I am looking at the knitpicks site right now and they have their yarn gauges listed in how many stitches in ONE inch rather than 4. So for your 13sts=4", that would be about 3.25sts/1". So looking at this page you could select the 'bulky' weight category, and then likely any of the ones come up will be suitable, depending on what kind of fiber you're looking for.