An interesting passage on yatagans
 

When I was reading a traveler account I came across a passage, narrating the comments of an Ottoman watching the parade of the new troops after the military refom in 1826. Though nothing new, still interesting reading:

"So these are the new troops" said he, "that I have heard so much of; these are the troops that are to defend the Ottoman Empire from its enemies! And what in Allah's name can the sultan expect to do with these beardless puny boys, with their little shining muskets? Why, they have not a yatagan among them! What does this mean? It was with the yatagan the Osmanlis conquered these territories; and it is with the yatagan they ought to defend them. The yatagan is the arm of Mohammed and of his people, not that chibouque-wire (bayonet) I see stuck at the end of their guns. Mashallah! And what sort of a monkey's dress is this?

The old-timers always grumble, grumble, grumble...
The era of the sword was coming to an end. Firearms beat them to a punch.
Ottomans were quite late to recognize it and as a result lost several crucial wars (and the whole Empire ...).
Starting at about that time they invited the Germans to re-organize their military; the new swords were pretty yucky, but the seeds of future victories were planted. In the immortal comment from the "Graduate" ,I have only one word for you: Gallipoli. :)

I don't want to be taken as a romaticist ;) It is just very interesting for me how yatagan became a distinguished symbol for the old order while the new order was symbolized with bayonet. Beyond these symbols, of course, what was at the stake was completely a different issue.

I was thinking if yatagan became the symbol for the old military order, did their manufacture come to a sudden halt in Istanbul after the 1820s?

Oh, no!
There are many, many yataghans dated second half of the 19th century. Many gorgeous ones, so your Old Turk was just a "Negative Nancy": Yataghan remained a symbol of Ottoman masculinity for a long time!
I do not recall seeing any of the 20th century (maybe one or two).
But then, again, Yataghans were produced in a multitude of former Ottoman "colonies" and I would guess that they got extinct even later....