You really can't blame the current Winchester for not wanting to back previously manufactured rifles.
If you just took over a company, would want to be in the hook for all the guns built over the last 150 years.
They probably have to back everything for a certain time, unfortunately for the OP, his ran out.
I have been told, automakers have to parts support their products for a certain time.
They should back it up or change their fu cking name.... Something like Portuguese Arms or something....