Doing some more research, I have the following info:
* hydroquinone -- UN 3077, packing group III, "limited" inner quantity exception: 5kg (1L as a general rule), "excepted" inner quantity exception E1 (30ml/30g), "excepted" outer quantity exception for outer packaging (E1) 1kg/1L. Special provision 335 might apply for amounts greater than 10ml/10g of solid??
* propylene glycol -- not regulated
* sodium sulfite -- not regulated
* sodium/potassium carbonate -- not regulated
* benzotriazole -- (surprisingly) not regulated
* potassium bromide -- not regulated
* sodium/potassium oxalate -- UN2811, packing group III, "limited" outer quantity exception: 500g, "excepted" inner quantity exception E4 1g/1ml, "excepted" outer quantity exception E4 500g/500ml.
* oxalic acid (potential substitute for oxalate in formulation) -- UN3261, packing group III. All restrictions (excluding provision 335) the same as hydroquinone
* ascorbic acid -- not regulated
The ideal kit formulation I can see would be premixed hydroquinone at 10% within the glycol, and with 5% ascorbic acid added as part A.The other chemicals excluding oxalic/oxalate would be in a part B-1 powder container. Finally, the oxalate/oxalic would be in part B-2. Basically this skirts the regulation by producing oxalate in-solution when mixed.
Now knowing this and with more research having been done, it seems that shipping each of these as powder would be extremely simple. Just the simple limited exception sticker on the box, sturdy bottles and bags for the chemicals, and done. However, for the end user I'd really prefer to mix the hydroquinone into the glycol beforehand to make it significantly easier to use. I'm unclear if these "liquid" limits apply to solids in a solvent, or if they only apply to actual chemicals that are purely liquid (such as glycol, triethanolamine, etc). I'm assuming I'd be using the "limited quantity" method rather than "excepted".
The other confusing aspect is that most photographic suppliers I know use ORM-D, but finding information as to if this would qualify for that is even more intensely confusing than limited quantity. Also it seems ORM-D will be phased out at the end of the year, so might as well plan to use limited quantity instead. It appears with limited quantity I do not need anything other than appropriately sturdy packaging and the stripe diamond sticker, as long as it's ground shipping only. (air requires proper hazard stickers and shipping documents).
Just wish I had a contact who has any kind of experience with this