Cabela's and Bass Pro Shops both carry 2lb mono and 2lb flourocarbon. Also, you can buy Stren in 2lb Hi Vis Gold so you could do the leader butt in a visible color if you wanted to. Personally, I like thread leaders better, but the 2lb mono is readily available.
Long as I'm already posting, might as well say that anyone who hasn't started furling because they haven't yet built or don't have space for a furling jig could just do what I do. My furling "jig" is just a 3 foot long piece of scrap wood I picked up one day. My "pegs" are four pushpins (I like doing 3-legged leaders because they seem to furl tighter). To twist the legs, I just use a Bic pen to pick the thread off the the pushpin (keep the thread on the wide, handle part of the pin, not down on the pin part), slide the thread to the middle of the pen, move the pushpin to the 90% length mark, and twist like when you were a kid winding up a rubber band powered balsa wood plane. (Yes, a drill would be faster, but I don't have a drill and I can't justify buying one just to make leaders.) When the leg shortens to the 90% length, slide the thread from the pen onto the pushpin. After twisting the third leg, pick up the other two legs so all three are on the pen, twist the pen the other direction until the leader has shortened to 80-85% of the full length, and then lift the jig to just past vertical so the pen can spin. When it stops spinning, tie an overhand knot on each end (before you remove the pen!). You can easily make each leader segment as long or short as you want, with as many threads as you want. I knot the segments together with a surgeons knot and trim the tags. If you use mono, you might want to put some Loon Knot sense or a drop of head cement on the knot. I use pre-waxed Unithread and the knots hold by themselves. Yeah, I know, I've got knots in my leader, but the knots never have to go through the guides anyway, and the leader performs just fine. Sure, it takes a lot longer to make each leader, but I don't have room for a full size jig and somehow I've found time to furl more leaders than I'll probably need anyway. One other advantage to this method is that you can make the leaders as long as you want. I've made several from 14' to 18' long to use as a flyline on a David Webster style Loop Rod. All it takes is more segments.