Assuming you mean the 2016 iPhone SE, in the US you cannot buy it from a retail store - it is not presently available on the market as new stock (that i'm aware of). You can only get them used, refurbed, or maybe NoS if you're lucky.
Not trying to be pedantic but where do you see this? I do not see the SE even listed in Apple's refurbished store anymore and I am struggling to find any documentation or evidence suggesting it is available thru Apple authorized resellers (no inventory I can find at ATT, T-Mobile, Verizon, etc)
FWIW I've been using a 2016 SE since... 2016, and I bought a spare one from Apple's refurbished clearance in 2019 when it became clear the phone would no longer be available outside ebay/grey market. If it's been silently available this whole time at any authorized seller that'd be huge news to me.
