"Broke" is not much of a description. When words fail use a photo.
I'll 'assume' (hate that word) that the head of the gib where the adjuster holds the
gib on location has snapped off or threads in the knee are stripped.
***Is the gib stuck in the knee or has it been removed?
New gibs that I have purchased have extra thickness and length, they have to be machined to proper fit.
Here are a couple of photos showing a new gib and a simple fixture.
A pattern of drilled and tapped holes are put in the gib. Then it is secured to the fixture.
The gib is held flat and straight and can be machined to suit.
New and used gibs cannot be counted on to be flat. Two gibs placed back to front might have consistant width, but that does not mean they will be straight. The fixture is a piece of hot-rolled that has been ground flat and square. A hole pattern to accomadate was added afterwards.
It is possible to remove and replace a knee gib without removing the table and saddle. The table must have the center of mass over the saddle. The saddle needs to be located towards the column till all the weight 'balances' over the knee elevating screw.
The hard part is removing contamination from the knee ways.
Try this company :
H&W - Parts for Bridgeport Mills, New & Used Machinery, DRO's, Power Feeds
Ask for Barry, plead ignorance and ask for help. I would ask if he could premachine a gib to nominal dimensions 'as new.'
John