Try pawn shops, garage sales, estate sales, egunparts, gun shops, gun shows.
Try gun shops, gun shows, egunparts
100-1000 USD
You have a browning a-bolt rifle chambered in .270 winchester caliber.
They did make .270 barrels for conversions of other firearms, but I'm unable to find any references to them ever manufacturing a bolt action .270.
You need the services of a gunsmith.
To find a bolt for a 270 model 770 engine, you can do so by looking at junkyards. It is possible that the parts may not be found online, or through manufacturers.
AFAIK they never made a bolt action shotgun
50-500 USD or so
IIRC, Winchester.
It will be marked on the barrel.
100-600 usd
It must be installed by a gunsmith.