Yes, there is a datafile you can import and install but the Harlequins are not in the original update 3.1x. It was in the AB 3.0 but I think they took it out and when I updated to 3.1b I noticed it was no longer there.
I decided to search for the Harlequin datafile, found it, and installed it. It appears to work with 3.1b with no errors but I cannot tell you if it is complete or not as I do not know there force organization well - but it seems to be all there
You can find this "unofficial" datafile at the Army Builders AB40k maintainers site. It is located in their "User Datafile" location (which means someone other than them made the file). Remember that you have to download it with Microsoft Internet Explorer (FireFox doesn't work at that site). Here is the link:
http://ab40k3.homelinux.net/modules...wdownload&cid=6&min=10&orderby=titleA&show=10
Enjoy