The best way to have this rifle repaired is to do a wed search for "Air Gun repair" and locate someone near you to have it repaired. There are several people/locations around the world who repair airguns for a living. I've sent out several from my collection to shops in California and had them restored or repaired. a model 250 ( Milbro) at best is worth $130. At least is worth $25 so you have to weigh the value of the rifle verses the cost of repair.
Best to ask a gunsmith for assistance.
50-250 usd
On line, gun shops, pawn shops
Try gun shops, gun shows, want ads, e-gunparts.com
This Rifle was made by Milbro of Scotland between 1965-74. Your best bet is to search the web for "AirGun Repair" and locate someone near you to repair the rifle. Milbro is no longer in production. No one sells kits to repair the rifle but I'll bet there are several repair shops around that can repair it.
ebay...craigslist...
No
22 250 Remington
There is no way of knowing,unless you provide the model of rifle you have that is chambered in 250-3000 Savage caliber.
50-250 usd
1965
$250-$375