Here’s what I found about fluoride. The recommendation is 4mg/day (http://www.iom.edu/Global/News%20Announcements/~/media/48FAAA2FD9E74D95BBDA2236E7387B49.ashx); though fluoride may not be essential. Generally, water fluoridation aims for 1mg fluoride per liter. There is a website that will tell you what level it’s at in your area if you live in the US: http://apps.nccd.cdc.gov/MWF/index.asp. If you’re consuming 3.7 liters per day, then you’re getting 3.7 mg, which is about enough. If you also use fluoride toothpaste, then you’re probably covered. Also note, if you use filtered water, it probably still has fluoride in it since most filters (which use carbon filtration) don’t remove it; though there are special filters that do.
Concerning black tea, I don’t think the tea leaves themselves have fluoride. I think the listed fluoride comes from the fluoridated water used to cook them (not certain though. Here they say no: http://nutritiondata.self.com/facts/beverages/4019/2). Same with oats (this site says there is no fluoride in oats: http://nutritiondata.self.com/facts/cereal-grains-and-pasta/5708/2). On the other hand, fluoride will generally be in any product you consume that was processed with fluoridated water, since the fluoride will be left behind after the water is removed. I don’t know which products those might be, but perhaps some of the things you’re taking.
All told, considering that the upper limit for fluoride is 10 mg, I don’t think you need to supplement with it.
Edit: I was wrong about the black tea. It’s got quite a bit of fluoride. How much appears to vary considerably.