(WSJ) - NOT EVERY GREAT wine in Napa Valley can exclusively be found in a winery; quite a few of the best bottles are also sold in local wine shops. Not just any wine shops, mind you, but places whose proprietors know the valley inside and out. Stop in for a visit or, better yet, a tasting and these longtime Napa residents will fill you in on promising new producers as well as long-established superstars—offering in one sitting a broad sample of Napa wines that might otherwise require weeks to discover. Here are four merchants to consider for your next wine-country trip, and if you can’t make it to Napa, they’ll deliver (where legal) as well.

750 WINES

David and Monica Stevens, the husband-and-wife proprietors of 750 Wines, are not only acquainted with every winemaker of note in Napa but seemingly every homeless horse, cat and dog. It’s not unusual to find animals from their Jameson Animal Rescue Ranch wandering around the St. Helena shop. On the day of my visit, it was a friendly pit bull named Gunner. “Why don’t you take her back to New York?” Mr. Stevens asked.

Tucked away on a side street, 750 Wines functions a bit like a private club. Although bottles are available for sale, the shop is largely a tasting venue. Tastings, which last 1½-2 hours, are free for up to six people. (Larger groups pay a fee.) Bookings should be made at least a month in advance, at which time would-be tasters will be asked to fill out a questionnaire about favorite wines and preferred varietals, price points—and music. This last item determines what songs, if any, will be played while you’re there.

Based on the other answers, the Stevenses will choose wines from their stock of limited-production bottles ranging in price from $19 to $225. The most commonly requested is Napa Cabernet, according to Mr. Stevens. Tasters are under no obligation to buy the wines, but given that many of the bottles offered here are hard to find anywhere else, most clients pick up a case or two. 1224 Adams St., Suite C, St. Helena; 750wines.com

K. LAZ WINE COLLECTION

Kerrin Laz, the 30-something owner of the new K. Laz Wine Collection, counts among her mentors the Stevenses and Leslie Rudd, a local vintner (Rudd Oakville Estate) who also owns a wide range of businesses, including, until last year, the Dean & Deluca grocery chain.

“Everything that’s here is because of Dean & Deluca,” said Ms. Laz. As a wine buyer with the company for almost 10 years she was in contact with some of California’s top winemakers. When she was putting plans together for her new venture, Ms. Laz reached out to 75 Napa vintners about buying their wines. All responded in the affirmative—a big vote of confidence, as the region’s top winemakers are quite particular about where their bottles are sold.

Like 750 Wines, K. Laz Wine Collection isn’t really about selling wine—bottles in the shop have no price tags—but about guided tastings. Ms. Laz offers three types: the Taster, the Artisan and the Cult. Each includes six wines from bottles costing between $40 and $635. Tasting prices range from $65 to $165 per person, depending on the caliber of the wines. Advance booking is required.

The Cult tasting I sampled on a recent visit included the 2012 Screaming Eagle Second Flight (the aforementioned $635 bottle) and, at the lower end, the 2013 Accendo Cellars Sauvignon Blanc ($54), made by famed winemaker Françoise Peschon. Other wines in the tasting included the 2012 Futo Oakville Estate Red ($335) and the 2012 Macauley Beckstoffer To Kalon Cabernet Sauvignon ($175), which was especially impressive.

In addition to wines that few ordinary oenophiles might encounter, Ms. Laz offers a running commentary about the people and geography of Napa—an invaluable insider’s perspective. 6484 Washington St., Suite C, Yountville; klazwinecollection.com