I have read of successful fire forming 22-250 brass, maybe a google search could get you going, Pretty sure 22-250 brass is somewhat available. You may need to buy factory 250 Savage ammo it may be your only route in these crazy times. Good luck!
Yepp. .250-3000 is obsolete and hard to find brass for. But its as simple as running .22-250 brass into a .250-3000 die to get usable brass. for that matter you cold also use commonly available .243 brass or .308 brass..
I personally would opt for milspec 7.62X51 nato brass because it doesnt have a caliber designation on the headstamp so you can minimize ammo confusion.
Fortunately I still have a good supply of brass -
I obtained a set of sizing dies to make 250 from 06 base brass - Most 06 base brass is suitable - some better than others.
My few test cases, 06 to 250 have proved to be somewhat time consuming. But, of course, this is better than no brass.
I do prefer to squish and neck ream over the stretching 22 to 25 --