I'm pretty sure that the (vast) majority of people making things out of circuit boards are using boards that have never been populated. You can see a lot of this stuff on Etsy for example. Reclaiming boards might be fine for low-volume, including special order production, but I'd think it prohibitively expensive otherwise.

I have no idea where these Etsy folk get their boards, wether they're overstock, failed designs or as Larry suggested, made for that purpose. A number of them have to be old stock since they look and are advertised to be "vintage."

It might be worth contacting some recyclers to find out if you can buy unpopulated boards. Seems a lot of places don't pay when taking unpopulated boards due to low quantity metal reclamation. So maybe this is an avenue to obtain such boards after all.