Not much later there was the Radio Shack Model 100, and a bit after that the Gateway portables, and of course, eventually the NEC Ultralite and eventually the Sharp PC-6220 (which was available under two other brands as well).

Also, for those with deep pockets there were the GRiD laptops....

None of those are 6502-based, though. I think that's why OP referenced the SX-64.