I ordered iodine crystals 5 years ago on a website thats now nonexistent, otherwise I’d post it as a source. The crystals last a long time and I have yet to add more to my box! I know people that got some off Ebay believe it or not. I was just writing that artchemicals.com listed iodine and may be a source but there site is not up now. I hope this is just temporary. Most art stores should carry rubylith. Rio Grande is great for solid sheets of silver to use as plates. Saw that on your list too. https://www.riogrande.com/home/
I’m using bromine. I got about 50ml of liquid bromine, works great. Seems like the bromine water should work just as good, its listed in the old manuals. I’m getting about 2 sec exposures outside with F4.5 – sunny.