Ich kann dir ein paar Beispiele für 'geschäftliche' Kondolenzschreiben nennen:

I am mourning with you for XY, who was a wonderful friend of mine for so many years. I convey to you my heartfelt condolences at X' death. I have long and fond memories of XY. My thoughts and best wishes are with you.

It is only today that I have received the sad news of the sudden/unexpected/untimely death of XY.

I would like to express/Please accept the expression of my heartfelt sympathy.
I wish to convey to you my deepest sympathy on the death of XY.

Ich hoffe, dass ich dir damit ein wenig helfen kann.

I am just writing to say how (very) sorry I was to hear about the death of SSSSS. She was a (wonderful, warm, lovely) person and will be (sorely, greatly) missed.
You are in our thoughts (and prayers) at this difficult time.

The comments in brackets are either optional or optional additions.

Passt zwar nicht zu Kondolenzschreiben, aber ich finde folgende englische Umschreibung einfach Klasse:
to be pushing up the daysies

Die habe ich im großen Pons gefunden:

I were greatly saddened to learn of the passing of Dr. Smith and send (or offer) you and your family our most sincere condolences

or

We wish to extend our deppest sympathy for your sad loss to you and your wife

Ein guter Einstieg ist auch diese Seite:
http://www.americanhospice.org/articles/condo...

for daysies read daisies!
for deppest read deepest