A friend is arranging a trip with some friends to Napa in September. He’s asked me for some suggestions.
About 10 yrs ago, for my birthday, I had tastings at Sullivan and Pine Ridge. But that was then. Thanks.
Also, not sure of their budget since tasting fees have now risen. This is for a serious wine crowd and not a party crowd.
I think Chiron can accommodate 10 people. Reach out to Bobby.
Also recommend Bell just outside of Yountville. Hit up Rob Vasquez there.
We’ve had almost that many at Quintessa. They have a nice little tasting area with a big table easily hold 10 people. They did a nice tour plus we had a little blending party too, where they brought in a few barrel samples, and we got to mix them in and make our own wine
10 is a big number, might be tough. Schramsberg, Alpha Omega, Venge definitely could.
Phelps, Chappellet, Pride, Cade, Arkenstone also come to mind.
10 is a big number, but if given enough notice, I think a lot of places can accommodate. I’d create your desired list, and start calling. If you are 2+ months out, you should have options.
Alpha Omega is the first that came to my mind - Cade also mentioned here could as well I think
You might try Rivers Marie. They have a table that would seat 10. They have great cabs, pinots and chards.
Great thoughts above.
Darioush could probably do that.
Napa Vintners Collective. I’ve been in a party of 12 there.
The Mayacamus in Napa probably could.
Kascandy might. I’ve been there in a party of eight.
Brasswood, easily.
(Alpha Omega already mentioned, is great. As is Chapellet. Rivers Marie, too)
You could got wild and likely get party of ten for Mending Wall in the morning and Davis Family after that. Both have great wines.
Best wishes!
I think there is a bunch that can host 10, at least they have space, rooms. Not sure how much food you would get. Call your favorite places. If I were taking a group, I would seriously consider Anderson’s Conn Valley (cave)- their tastings were a blast when I was there; Turnbull; Beringer Reserves/ SV’s. Plenty of options.
Hendry near downtown Napa off redwood road can support 10 and the tour is outstanding.
Stag’s Leap Wine Cellars can take up to 12 on a tour, esp given enough notice
Judd’s Hill could do that, and is at a good price point for casual wine drinkers.
I would try Sinegal. It is good for big groups and the wines are very good.
Cliff Lede can as well. Alpha Omega easily. Flint Knoll as well I believe.
Shafer…unsure what they’re charging these days if not on the list, but I recall they do tastings for 10.
Does your friend have a friend with a helicopter?
Nope. Not even thinking about landing at Screaming Eagle. 
And thanks everyone for the suggestions. My friend is going to try for Alpha Omega.
Plumpjack, Cade and Odette, if interested I can assist, owner is a long time friend.
Chappellet can do that size.
Thanks for the offer. If Alpha Omega doesn’t work out I’ll let you know.