[ksarul]

The SN76489 is not a direct drop-in replacement for the SN94624, as the SN94624 has a max clock speed of 500 KHz, while the SN76489 has a divide by 8 added to the clock input to allow the system clock to be working at up to 4 MHz. There are three chip designators you can use: TMS9919, SN94624, and SN76494--all of these have the 500KHz clock speed. I see one seller with the 76494s on eBay right now (there is also a US seller that occasionally has one for sale, but I haven't seen the one he had left up for sale lately, so he may have sold it).

The TMS9918A chips show up a lot--and even the Chinese ones are often fully functional chips. I don't have any spares at the moment of either chip, unfortunately.