Mica, thank you for your rapid reply!
I'm sorry, I should have specified - I'll be ordering some generic parts (a small spring-steel battery clip, some better strap buttons, a nut blank, and a piece of figured maple to fill a pickup route and a couple of unused holes) from a local supplier (Solo guitars in Concord, ON). They have a number of sizes available, but I can't tell if Alembic's proprietary components use the same thread size as other American companies, like, say, Bourns, which these potentiometers look a bit like. I have also never had anything with this type of switching jack. Do not worry about measuring the thread size, I was only wondering if anyone knew off-hand. I will simply try the nuts off other instruments with more familiar components until I find something that fits, then I'll know what size to grab.
Thank you once again for the response - it's not often you ask a question on a forum and get a 1-day reply from a close relative of the brand's founder, but I suppose this is Alembic, after all! Very finely crafted electronics, but the way. I'm looking forward to hearing them in this bass.