Keepsake Quilting sells a few of the tops, and the quality is good. If a person wants to try wholecloth quilting, I suggest very strongly that he or she get a SMALL piece rather than a bedsize top! Keepsake sells a round (with shallow scallop edge) piece with holly leaves and berries that is a great size not only for seeing whether one really enjoys doing wholecloth work but also for practising the stitching itself. If a quilter decides that wholecloth quilting is great stuff, that's great -- go for larger pieces! If a quilter decides what wholecloth is a bunch of hooey, there's not a lot of money or time wasted.
Another suggestion is to make a pillow cover. You will need a pillow form, 2 packages of bias binding tape in a color you like, a zipper to match, low loft batting scraps (enough to cover both sides of the pillow), white fabric (enough to cover both sides of the pillow twice), and brightly-colored quilting thread. (You can use a different color on each side to try different colors.) A lot of that stuff you probably have sitting around anyway, right? So save some money and use it up! Cut 4 pieces of fabric to fit the sides of the pillow, plus 2 pieces of batting of the same size. Get out a plain old No. 2 pencil and mark your stitching patterns on 2 pieces of the fabric -- with stencils, free-hand, anything you like! If you mark with light to moderate pressure with a fairly-sharp pencil it WILL wash out! Assemble the 2 quilt sandwiches, baste them, and begin with the wholecloth stitching. When finished with that, attach the seam binding around the edges of both quilted blocks, sew them together on
3 sides, and attach the zipper. Now go toss it into the washing machine and dryer! Stuff your pillow form inside, zip it up, and toss it on the sofa. I always make a pillow to test out colored threads I'm considering using since they always seem to handle and look differently than expected, and I never want to begin an entire quilt with thread I don't enjoy! It's also a very good way to test out a white fabric that is new to me -- they are all a little different. And another pillow? They're good on the sofa, in a chair, and on a guest room bed. My new sofa came with a pair of really comfortable but really ugly pillows, and I made covers for them!
I really enjoy wholecloth work, and go about it rather unconventionally. I work in small pieces which are later joined to make a quilt, and attach them with thin strips which makes a window- pane effect. I also work in colors, so the fabric is white, the thread is a bright color, and the joining strips are another bright color. My wholecloth work is thus portable, with a few blocks tossed into my tote bag along with thread, needles, etc. for travel.
As much as I enjoy wholecloth work, other people don't like doing it at all, so do make something small as a test before investing your time and money in a big way!