Options to read an 8x8 switch matrix?
I wouldn't try to get too clever, you'll just make your circuit more troublesome in the long term. Do you really need a switch matrix? Why not just use multiple port expanders or shift registers? Those should be fast enough. If not, many come with an interrupt output which you can hook up to your micro to make it INSANELY fast. That will also eliminate the polling overhead. If you can get away with a micro that has a lot of IO, like the Arduino mega I would go with that instead.

Many port expanders and shift registers are available in dip packages. For example the MCP23017-E/SP 
https://www.digikey.com/product-detail/en/microchip-technology/MCP23017-E-SP/MCP23017-E-SP-ND/894272

And here's a shift register you could use: CD4021B https://www.digikey.com/product-detail/en/texas-instruments/CD4021BE/296-2040-5-ND/67261

You can easily daisychain multiple shift registers together to get as many inputs as you need.

Tutorial: https://www.arduino.cc/en/Tutorial/ShiftIn