[Does anyone have any advice on how I can get the gun fixed?]
As you have found out, Ruger will no longer support the old model .44 Auto Carbine for either parts or service.
You "might" have a broken trigger housing.
If so, it is an unrepairable item, generally unobtainium, also - but it'll be better to find out now if it's that or a worn latch, etc.
Their trigger housing's have a small/male lip at it's forward/upper end, that hooks into a recess in the underside of the front of the receiver to anchor the housing while the large crosspin anchors the rear.
When the lip's gone or cracked, the front of the trigger housing "floats" during cycling under actual firing, misaligning the feed parts and resulting in mis-feeds, aka "jams".
The best way to check the lips is to take the rifle apart, as per the owner manual, and visually inspect the lip for cracking or gone missing.
The 2nd best way to to try to check for play with the rifle assembled in it's stock.
With one finger inside the magazine throat and the thumb outside the bottom of the front of the trigger housing, work the barrel up/down.
If ANY movement can be felt between the barrel/receiver and the trigger housing, it's a pretty good bet that it's a gonner.
It the housing's still good, then the problem is most likely in either worn latch parts.
BTW - There hasn't been any lead boolits fired through it, has there ? Even only a few ?
If there HAS, there's a very good possibility that your misfeeds are the result of a partially lead-clogged gas system.
THAT fix is a total tear-down & scrub-out.
Good Luck
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