Why is it "ode" and not "od"?
This is a variant of "od" which occurs in only a few situations. The most common expressions are "ode mnie" and "ode złego" (which occurs in Lord's Prayer). Analogously, we say "beze mnie" (without me) but in other cases it is just "bez" (without).
Why cant it be "buy me something"
Because it's totally different. In the Polish sentence, I am selling something and I want people to buy something from me. Not buy something for me.
I have written a correct answer but it is not being accepted!!!
That does happen sometimes, unfortunately.
Surelyod would be well understood
"od mnie"? Even for a Polish person it's hard to pronounce.