I have a few annoying Xiaomi devices that like to find Zigbee repeaters (wall switches) that I would have made Z-Wave if I have known I was going to use these years ago.
Anyway…
I was looking to get some ST branded water, motion and arrival sensors and do you think I can find any of the traditional devices on one site?
Samsung.com does not have the product range, no motion or arrival!
Samsung.ca here in Canada has missing devices.
Most resellers have this and that at random.
I know Samsung is not in the hardware game anymore but you would think the core products would be available for order.
Look at ebay. I’ve seen some Arrival (presence) sensors recently for 20 USD from ?BestBuy?, I am not sure.
You might can find the other devices as well.
Be aware that support in Canada has recently started being very strict about which retailers they will honor the warranty for, and have even been refusing warranty service for devices bought from Amazon! So to be honest, I don’t know what to tell someone who lives in Canada. 
Amazon in both the US and in Canada is carrying most of the devices (except maybe not the arrival sensor) as stocked and sold by Amazon. So since the product descriptions do give the regular warranty., Amazon should at least take a return if there’s a problem. But I can’t guarantee that would happen.
I used to order from the USA without issue. I find the discrepancy between most large manufacturers when they make regional sites to be too great; one hand never knows what the other is doing and the sites are often soooooo out of date.
I’m not worried about warranty as I don’t often buy ‘grey’ market, if I do I’m cognizant of the risk.
Amazon is a strange world. Sometimes you find what you want and other times a 39.95 product is listed for 495.00 and 70.00 shipping from “these suppliers”. It’s a waste of time for fringe items, I would rather just buy from the main vendor.
Just wish a major brand would list all of their products and, if any are unavailable, don’t delist them but mark them as ‘Out of Stock’ or "Unavailable’.
End of small rant
Understood: I don’t buy from third-party resellers on the Amazon platforms either. But I do buy items which are sold by Amazon itself or by the device manufacturer and fulfilled by Amazon. But not “AButifulDay” or some other random third-party who may just have fished the device out of a dumpster. 
The sensors do seem to be available from Amazon itself, probably because they work with the Amazon echoes that have a zigbee hub inside. I can’t say whether that new stock or inventory that they’ve had for a while, but they do seem to have it available.
Someone mentioned to me that some items are not for sale by samsung because they havent gone through the work of getting cerification for items that arent big sellers, so we are stuck buying from 3rd parties for now 
In general Xiaomi devices prefer IKea Tradfri repeaters (because they are not standard Zigbee devices).
You might be further ahead in getting Konke, or Tuya, or ZemiSmart, or Blitzwolf, or Zemismart, or Heiman Zigbee 3.0 devices. Available from alieexpress.com