You said it. It seems the demand is there. I doubt it's big enough. 

       Joe.

Starline has 32-20 brass, one pass through your 25-20 sizer should make 25-20!
The Starline site says it is available now.

Don't bother contacting Winchester - you won't get an answer. I already tried when I was asking for 218 Bee Brass as well. They say it is a "Seasonal" production, but for them seasonal means every 5-10 years I think. 
As an example, I had a buddy call me to say that Buffalo Arms had 218 Bee in stock (he was mistaken), when I called they just laughed and said that 25-20 and 218 Bee has been backordered with Winchester for 4 years...

I also inquired at Starline why they do not produce 25-20 or 218 Bee because every forum I am on has people looking for it. I was told that Starline does not have the annealing equipment, so any necked case beyond 32-20 can't be done. The problem with necking down 32-20 is that the case will be short after forming. It will work in a pinch, but is not optimal.

I've made plenty of 25 20 brass from 32 20 and it comes out the same length as 32 20 as it should be.  I had some necks fold as they were reduced in size if I tried to go directly from 32 to 25 caliber so I put in an intermediate step of first reducing to an intermediate size by in my case pushing them into a 7mm Mauser die.   I built a push rod that fits into the shell holder on my press that pushed the case into the neck of the 7mm die.   I use the 7mm resizing die with the depriming rod removed.  then a brass rod to knock the case out of the die.

I suggest annealing the 32 20 brass before necking down and use plenty of lubricant to help avoid neck folding.

I've had only short waits of a month or so getting 32 20 brass from Starline.

Bobduck

Baja_Traveler wrote on Oct 11^th, 2015 at 9:27pm:

There's a guy on Cast Boolits, GRUMPA I think his name is, that sells .25-20 made out of .32-20.  Look in the For Sale section.