csup is usable for a cvsup client, and since it’s written in C, doesn’t require modula-3, which doesn’t build on DragonFly.  csup was broken on DragonFly, though YONETANI Tomokazu has a fix.  Of course, the server side still needs to be compiled, with the same dependency problems.  Alternatives like cvsync have problems, and rsync is supposed to be too taxing, but now is a good time to test that assumption, perhaps with a benchmark?