Is this anywhere around New England? It keeps popping up in the cellaring forum, but I've never seen it in stores. If this is one of those, "That's because it's impossible to find" things, my bad. I'm clueless.
The only place I've ever seen it is at Charles Street Liquors. I imagine most stores simply choose not to purchase it through their distributor. Saw it a few months ago when I last poked through Charles St's British imports, but I would not be surprised if your JW Lees remained on the shelf there. There's pretty low turnover on their imported stock. The relatively-high price dissuaded me from buying it at the time, though I am similarly-curious to try it at some point, given all the love it gets in the Cellaring forum.
I saw a few bottles at Vinnin Square over the winter, when I decided to pull the trigger and buy them, they were gone. I'd say you should find them somewhere, and if you do, don't hesitate if you want them.
A couple of shops in Burlington, VT have it from various vintages and barrel treatments. Been fighting the urge to buy out shelves for a while now...
Their importer sells a mixed case of different vintages/wood treatments of this beer. It's a special order item, but any solid craft beer store should be able to special order it. OP, if you're interested PM me and I'll let you know where it should be available on shelves at the moment.
Perusing various import sections in CT I can usually find the standard Lees though they tend to go faster than the various barreled offerings. They also tend to retail around $10/11.2oz IIRC and if you're in the market I can keep my eyes open.
Just picked up a bottle of the Port BA version at Bier Cellar in Portland. I've seen the Lagavulin BA version at Tullys in Wells too.