D&R Marine sells the Cruising Design Flexible Furler, we had one on our CAL 21 and it worked pretty well. I have not added Roller-Furling on my DS II yet, still like the simplicity of the hank-on jib. If all you are looking for is simple roller-furling, and not reefing, you could get a jib from a DS III (basically the same as the DS II but the DS III had roller-furling on the jib) and buy a set of the upper and lower swivels (I actually have a set). This is not an ideal setup, the CDI furler from D&R is much better and really not much more $$ in the long run!
I found a DIY furler on the COMPAC 16 web site, but you would need a smaller jib than the standard DS jib, since that setup has to be much shorter than the forestay (DS jib is only about 6" shorter than the forestay) It was made using PVC pipe.