You could just use a CGA to VGA adapter I think can't you? I don't think there is any reason to get another isa gfx card unless you just feel like it.

either get another vga and use the lpt port on the i/o card (or an extra lpt card) or just get the cheap converters as suggested above, they are dirt cheap now: http://www.ebay.co.uk/itm/301250849489

Unless you specifically need the parallel port on the old graphics card, I would replace it with an ISA VGA card, and just hook it up to a newer monitor. Assuming it's a DOS machine, it shouldn't make too much of a difference. If it's running Windows 3.x however, then you may need to run Windows Setup to change what graphics adapter it's set for.

I was just looking at the adapters they were selling on eBay, and they look far more sophisticated than the DB-9 to VGA converters I've seen. It may be worth giving one a try, especially if you don't feel like fooling with how the computer itself is set up, though I wonder how well the adapter itself can actually handle CGA/EGA signals.

Either way, you'll be able to use a newer monitor, and not have to deal with the old, broken CRT. Repairing CRTs is kind of a dying art, as most people don't have much of a use for them besides retro gamers and other people who are fascinated by vintage technology.