Varan, I'd suggest you just go looking for any photo lab or shop. That's what I did, and found one less than a block from my hotel. I guessed that good cameras would tend to be used for a lot longer time in countries less "consumerist", and it seems I was right. while 120 film was about obsolete in European high street shops, it was still alive and well in most of Africa (well - the parts I've been to).
Today the situation may well have changed, as any film seems on the way to obsolescence - at least if you believe what you read on some photo sites. For all I know, 120 film in Egypt has gone the way of the dodo. And maybe that shop has, too - there could be a new souvenir shop there, or a high-rise hotel, or something completely different. And maybe it wasn't on the Qasr el Nil in the first place; my memory is no longer what it's never been.