Re:
"For instance the part about "only has to run at about 1900 C" is a bit puzzling. "
From:
http://www.suppliersonline.com/propertypages/309S.asp
"Stainless Steel 309S:
Superior corrosion resistance to 309 in the range of 800-1500 F (427-816 C)

Applications: Oven linings, boiler baffles, fire box sheets, furnace components and other high temperature containers.

Working temperatures are 2150 F (1177 C), with reheating necessary at 1800 F (982 C). Rapid quenching is recommended. Full post-work annealing is required to reattain maximum corrosion resistance.
Annealing: 1900-2050 F (1038-1121 C), water quench. "

So, to shape/fabricate 309 stainless you need 1177 C, and to set it's temper 1038-1121 C. In a words, 1900 C is far too high temperature for 309 stainless steel- in space, I would guess it easily boils at that temperature.

Now platinum, has high resistance to temperature and very resistant to corrosion
But without any special alloy it's:
"Melting Point: 1774 degrees C & 3225 degrees F"
http://jewelrymaking.about.com/od/metaljewelrymaking/a/032605.htm

So pure platinum in space would also start to boil below 1900 C.

Now rocket nozzles are going have to be highly heat resistance, I'll do a search [I can't remember exactly what is used]

The so-called superalloys are materials designed to function for extended periods of time in highly oxidizing and corrosive atmospheres at temperature above 650°C. Superalloys represent the second largest use of niobium outside the steel industry.

"There are literally scores of different superalloys used in a variety of high temperature or corrosive environments. However, the single most important member of the class is Inconel 718, a nickel-based alloy containing 5.3-5.5 wt% niobium. This alloy forms the backbone of commercial and military jet engine manufacture. The most common jet engine in service today, the CFM56 made by the GE/Snecma joint venture, contains about 300 kilos of niobium. Most of this niobium presently comes from CBMM’s Araxá mine."

And more specifically:
"Niobium-based alloys are also used as refractory materials for aerospace applications since they have excellent high temperature strength above 1,300°C and readily accept coatings to protect against oxidation. The most important alloy in this case is called C-103 (a niobium-hafnium-titanium alloy) used mainly in rocket thrusters and rocket nozzles. Consumption of this alloy has recently increased due to booming satellite launching activity. C-103 is always used as a skirt on the Pratt & Whitney F100 engine, a high performance power plant used on fighters such as the F15 and F16."
http://www.us.cbmm.com.br/english/sources/uses/use&user.htm

Now, I'm remembering, nickel. And of course titanium alloys.

Anyways, 1900 C is not easy.