I can't help with the Sulky, although if you google it you will probably find online stores. Bottom Line is made by Superior and can be purchased at their website
www.superiorthreads.com. I also purchase it from local quilt shops in my area. You might check
www.fabricdepot.com, they carry both brands. If you sign up for their e-coupons you get 35% off one item every week. It can be challenging, finding stuff on the website, but their customer service is excellent, so if you can't find something, just call them.