Big thanks to Cagey, Grady, Packard and Parla, thank you all for your valuable input. "Join the crowd", and "Welcome to the club", these are exactly the expressions I've been looking for. Must have heard them several times when watching American TV series and movies, but didn't purposely try to remember them.
Here's the actual situation, more like what Packard described in the example email: I was chatting the other night with a Chinese client who is also a friend now -here's another question: are there some terms to define such a relationship, maybe a "client and friend"? - and he mentioned this lens that's currently very popular yet out of storage at the same time. The next batch won't be available till next February and there won't be plenty. In the meanwhile there are already a number of people on the waiting list. So I wanted to warn him about the situation, in Chinese of course. But this just reminded me of the English sayings I came across before.
Normally I wouldn't say something like this to a client I don't know well. Yes, as Cagey suggested, there's a hint of sarcasm in the tone. I have no intention to drive away a potential client like this. Packard's message sounds more formal and appropriate, thanks!
I just like these vivid and maybe colloquial expressions like "join the crowd", or "welcome to the club"! They are the beauty of a language for me. Thank you, Grady and Parla.
Thank you all for being so informative and helpful in a timely fashion. I've learned more than I expected: )
Dorothy