Hey, I came here to ask this too! I think I have a partial answer: When they first launched, I definitely remember the hinge connector having options on its page to purchase the two halves separately or as a pair. However, this doesn't seem to be possible anymore. Moreover, I noticed the parts pages have been slightly reorganized in a few ways, (e.g., adding ½" options for most connectors, condensing the 'Pro' (1" EMT) & 'Standard' (¾" EMT) T-connector pages to one for both with size options). This suggests to me 2 general possibilities:
(1) it's a temporary/accidental issue. The option to buy the halves of the hinge separately may have gotten lost in the redesign of the pages, and will be restored once Jake/David/Kelly/? reads this post and is able to restore it somehow. Something like that, anyway.
(2) it's intentional and the option was removed on purpose in order to keep inventory levels of the two halves in reasonable balance. This would be odd but like. I'd get it?
Option (2) seems very unlikely given the context of them having designing the new part to fit the half you and I (and I suspect others) would like to buy, so imma go with some variation on (1) being most likely, and so am resolving to look forward to that option opening back up in some form, maybe if we're lucky even soon :)
PS: I H*ckin' *LOVE* these new parts, they're so well designed and much needed. Got a dozen in the cart, can't wait to find out on this subject either way to slam that order button 😁