David, have you thought about contacting a stone carver who works with basalt? It sounds like the pieces you're looking for would be fairly small.
Surely they would have some 'tailings' from large sculptures that they'd be willing to part with.

Here is a link that might be useful: some california stone artists

David find your nearest concrete batch plant.
They sell aggregates by the pound/ton from sand to 100 pound boulders and even bigger.
You can usually drive up to the boulder piles and handpick what you want and get them for pennies per pound.

I'm not a rock guy but I did this to get a pickup load of green rocks and it cost me $8 for 800 pounds.

What about contacting a headstone carver and seeing if they have leftover small pieces they want to give away.

Lots of basalt lava flows in Oregon/Washington ....near the MacKenzie Pass area in Oregon....I am also including a link to some Google listings

Happy rocking

Vicki

Here is a link that might be useful: Basalt places in Oregon

Thanks for the info. Just knew someone would know where to snoop. GB

Hi, just peeking in here and saw this thread - if all else fails, come up to the Columbia River gorge on a field trip. We have nothing but basalt everywhere. Every size, color, shape you could ask for. And you get to visit the scenic Columbia River Gorge in the process.

David, Are the columns you refer to the hexagonal crystal shape? I saw an example of this feature at Devils's Postpile National Monument which is on the far side of Yosemite, south of Mono Lake. It may be protected from rock hounds, and I think the crystals may all form at a specific size, but it is a wonder to see!

Here is a link that might be useful: Devils Postpile