Well, I worked some of this out.
The ball-joint pinch bolts are 10mm diameter, 1.25 pitch, flange type head (and flange nuts too), 55mm length, but the kicker is that they're 12.9 grade. That's the insanely strong, probably 20% or more stronger than "grade 8", and nobody, not even the specialist fastener stores, seem to be able to get them as stand-alone items in this configuration.
Well, the local Nissan dealer has them, but their list price is $16 for the nut, and I think it was $7 for the bolt (yeah, you read that right, nut's twice the price of the bolt, but the nut is what the book calls for replacing every time!)
NAPA sells a balljoint kit, which includes a greasable balljoint, and the nut/bolt, for about $40.
Other than that, I can get a 12.9 grade bolt that's 60mm long, 1.25 thread and 10mm diameter, but only in a cap head with allen/hex head, not with the flange, nor with a regular hex-bolt head.
I plan to go for the latter option, along with washers. Such bolts seem to be under $2 here: https://www.fastenal.com/products/details/0154272
They're also available to me locally in Denver from AAA Metric, I'm told (I'll find out if they're as good as their word tomorrow...)