The most common and most likely answer to this crossword clue is the 6 letter word BUSIER
I've seen this crossword clue in The Times
B
U
S
I
E
R
More clues leading to the result BUSIER
Buddy explains!

The straight part
We know that "less available" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case less available = busier.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 BUSIER mean?
BUSIER adjective- Crowded with business or activities; having a great deal going on.
- Engaged in activity or by someone else.
- Having a lot going on; complicated or intricate.
- Officious; meddling.