I don't know of any right off the bat but I have to commend you on your selection. I'm currently building my boy a gun , I'm using an Encore so I can start him out with the 22 LR then move up in caliber yet maintain the same "feel" for him , the bigger caliber is gonna be the 250 Ackley improved with a 22" light varmint conture barrel , which is the same conture as the 22LR thats on it now.
The Encore is a great gun for kids to start with cause its light and the stocks are easly modified to fit them and it will allow them to shoot both right and left handed if they haven't figured it out yet.
a little cheaper way to get an Encore would be buy the complete gun in say a 243 which is every bit as good as the 250 with the proper bullets
You can buy "Bantom" (12 1/2 LOP) stocks directly from T/C for the contender and Encore carbines and rifles.
I do not think any manufacturer makes the 250 particularily in a youth gun.
However, here is a trick if you can find any 250. take off the recoil pad and drill two 1/4 "holes about 3 inches deep in the butt. tape the stock and then cutoff how much you need. Save the piece you cut off so later when you want to lengthen the LOP, you simply get two 1/4" dowels and glue the piece back on the stock. It will match perfectly. Light sanding and touch up stain and finish and it is ready.
The 7mm/08 is great round also. You can work up light loads and use the 120 gr bullets. I started my daughters on the contender carbine in 7/30 waters and then went to a 4.5 lb Ultra Light Arms 7mm/08.
I think current productions for a 250 savage is out, but you can always go straight to the horses mouth. By a savage or stevens youth model with a short action caliber that you may like in the future, then get an after market barrel in 250 savage. Swapping barrels on them things is a relatively easy task.
Remington makes a .250 savage in a model 7 MS (Mannlicher Stock). Of course, from the custom shop only. I bet it is big bucks.
I would search around for a savage model 99. You should be able to find plenty. They only stopped making them a few years ago.
I have a model 99 take-down in 250 savage. It is perfect size for a smaller shooter. My grandmother learned to shoot with it, then my mom learned to shoot with it, my wife learned with it. Someday my little girls will learn on it.