Frontier Optics (
www.frontieroptics.com) sell UO products.
You can buy directly from UO from
www.universityoptics.com to save a few bucks perhaps (so I've been told), but Daniel from Frontier Optics has been great with me via email, and his prices are very reasonable. And while you are there you might want to consider getting the 12mm HD ortho eyepiece, which barlows to a 5.5mm in that barlow (in a typical 2-to-1.25" adapter; you get more mag with an extension piece, less with a low profile adapter). The combo makes for a superb high contrast high-mag planetary eyepiece. Eye relief of the 12mm HD is quite good on its own, and even better when barlowed. Televue 15mm Plossl is also superb in that barlow for high contrast mid-high mag planetary viewing.
Dave (47Tuc) did a review on this barlow for the site. Check it out in the Reviews section. This is a big barlow, and it needs to sit a fair way out of the focuser. Have a look at Dave's photos and make sure you're comfortable with the bulk of the thing.