My first call is to bring out the backup clock!
I think what you did was reasonable. A player/coach certainly can't claim that they were unaware of the time remaining at the buzzer (which they could if they weren't looking at the clock). (BTW, how long was the shot clock period?)
Assuming NCAA rules, this seems legal (at least by last year's book) 1-18 requires two visible shot clocks, but mandates that some alternate timing device be available. If one wanted to be anal about this, they could say that the alternate timing devices must also be visible and, therefore, the game could not be played.
If the scoreboard allows, and if it is in a location such that it would be visible to all, you could use an empty score/foul count/etc spot to count up to 35/30.
If the shot clock console is completely burnt out, we have no stopwatches, and no announcer, I would probably say that we're going by the game clock - the shot clock operator could (hopefully) subtract the shot clock period from the game clock, and call out the time at which the "shot clock" would expire. He could also provide a countdown from 10 or so.