Promote to piece other than queen (in otb games)

I haven't seen it happen in an otb tournament so I'd like to know: if a player wants to promote to a knight/rook/bishop but there is only an extra queen piece, how do they go about doing it? Obviously in informal/club games you can turn a rook upside-down, or agree the spare queen is something else, but what happens in official tournament situations? Do the arbiters carry spares in their pockets!?

Promotions usually occur late in the game, by which time some boards have finished, you just grab a piece off a finished board.

you find  a piece captured on another board, or use your already captured piece you have

If you don't have a spare piece, you may stop the clock, call for an arbiter and request it. Running to another board with your clock ticking is highly unprofessional and irrational.

Question answered. Thank you :)

Also, I suppose you'd usually only do such a thing if it would achieve a mate - in which case your opponent would resign before the piece needed to be found. 

But I'm enjoying imagining Nakamura needing a knight with 5 seconds on the clock and having to wait while the arbiter goes to find one (perhaps with Carlsen sulking on the other side of the board).

This was a good question, I never thought I may find myself without a piece, now I'd simply move my pawn to the 8th, say "knight" and stop the clock   I remember reading some dispute where a player wanted to promote to a queen, and grabbed a rook to turn upside down, and the other player claimed that because a rook was touched off board that the player had to promote to a rook... I think the TD agreed and made it become a rook even though the TD made the wrong call, it's nice to know the most professional thing to do is stop the clock and request the piece.

Who won?

umm... any reason he chose a bishop? lol maybe to practice the mate not realizing he had 2 dark square bishops heh.

lol

Probably a mouse slip.

Let's suppose it was a mouse slip and White immediately realises his error but in his shock has another mouse slip. This time he resigns instead of offering a draw. Would that stand? Black has no way of winning but resignation sounds awfully final.

I've had underpromotion come up a couple of times in over-the-board play, but this was in informal play. Mike's last chance was the queen promotion that would stalemate him. I move the pawn, announce "rook"--and before I have to worry about finding an actual rook, Mike slams his fist down, wipes the pieces off the board, and exclaims, "how could I not win that game?!"

Brilliant. THIS is why finding an extra piece is never an issue ;)

Here's a relevant line of the Albin CounterGambit:

It happened with me sometimes, in informal games. When there are no extra pieces I just lay the pawn down and claim it's a new piece.

Pretty sure you can "declare" the pawn as the promoted peice. I see this done in blitz. Just say it aloud.

here is one that I am sure is sound, normaly I use a quarter or my old student ID, this was played on this site, but I have promoted to knight a few times OTB, mainly because of forks.