I've just finished uploading a whole bunch of deer tail brushes to my etsy page. There are a variety of sizes available and they all ship for free in the US. Generally speaking the fuller the brush the floppier it will be and will tend to leave more gestural marks. Straighter tips will tend to be less floppy and yield better control but will not give as loose of a mark. If you have questions about the brushes or need advice on what may be best for your application you can convo me on etsy and I'd be happy to help you figure it out.
Here is a picture of the brushes I use. I've been using these for about 4 years, the two on the left make all the stem/leaf type patterns as well as some line work. The middle brush is much smaller and stiffer and it's used for small lines and banding, the fourth brush is used for large leaf type marks as well as for laying in glaze. The last one is used for applying glaze dots. One might think that I saved the cream of the crop for myself but these were all brushes that had some sort of flaw, seconds if you will. The first two have brush tips that were too small for the openings, even though the epoxy holds them in place just fine, they look a little silly. But they do the job just fine.
You can see my etsy page here.