Possible substitute yarn

You can get all the yarn you need at www.Herrschners.com
They still sell the Red Heart Super Saver black (#0312) and White (#0311) at $3 for 7 oz;
they sell the Red Heart CLASSIC "Wedgewoods" (#0972) for $2.70 per (I think it's 3 oz) skein;
and they now have Herrschner's 2-py Afghan yarn for $1.70 each in Berry Delight (#0103) and Teal (#0039), which, if you tweed one strand of each, will give you just the right look for the half circles.