So who were the other six?

[Frayed Knot]

... 3 HR guys that is?

It's a record now held by 7 Mets.
I'm sure they mentioned the entire list on the air -- but by that point I was only sorta watching and not really listening.

Jim Hickman was the first. And I personally remember Kingman, Carter, Strawberry & Alfonzo

So it looks like I'm missing one.

[metirish]

Claudell Washington in 1980 IIRC in what Gary said.

[Frayed Knot]

All seven occured on the road.

Reyes - Philly
Alfonzo - Astromdome
Straw - Wrigley
Carter - SD, I think
Kingman - ?
Washington - ?
Hickman - ?

[Guest Yancy Street Gang]

Yes, all 3-homer games were on the road:

Hickman, 9/3/65, St. Louis.
Kingman, 6/4/76, Los Angeles.
Washington, 6/22/80, Los Angeles.
Strawberry, 8/5/85, Chicago.
Carter, 9/3/85, San Diego.
Alfonzo, 8/30/99 Houston.
Reyes, 8/15/06, Philadelphia.