The most common and most likely answer to this crossword clue is the 10 letter word LUMBERYARD
I've seen this crossword clue in The Guardian
L
U
M
B
E
R
Y
A
R
D
Buddy explains!
The straight part
We know that "Where deal may be had" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case where deal may be had = lumberyard.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LUMBERYARD mean?
LUMBERYARD noun- A facility dedicated to the preparation and/or sale of lumber.