Using LC server to check for existence of mp3 on our web server?

[Tim Selander]

Hi,

On-rev.com hosting, using LC server to present a list of our 
AM/FM radio programs for people to listening to on-demand.

Out of a month's 20 programs, 3 or 4 might not get uploaded due 
to copyright issues, etc. Also, mp3's are not on the on-rev.com 
server, but another hosting service we use as well.

Filenaming is standardized, so I know the list of programs. I 
want to hit the server, if the mp3 files exists, present it as an 
<audio src=, if the mp3 file does not exists, present a "Sorry, 
program not available" message.

If I wanted to check on the existence of a small text file, it 
would be fast enough for me to just get it, put it into a 
variable and see if the variable has anything in it. But mp3's 
are too big, so too slow.

Locally, I would simply write "if there is a file 'filename'..." 
  -- what's the equivalent command for checking on existence of a 
file on a server?

Thanks in advance.

Tim Selander
Tokyo, Japan