MCA was IBM's proprietary solution to the limits of ISA, EISA attempted to be the industry standard, through most of the 386 era 16-bit ISA was tolerated and during the 486 VLB won out in the consumer space and the Pentium era ushered in PCI, although some late 486 boards had it, they're not particularly common, maybe still more common the EISA. EISA though is harder to find because the machines are either still in the store rooms at businesses or they got recycled, also the market for them was business and large businesses probably didn't buy as many EISA systems because the high end server and workstation market wasn't completely dominated by the PC yet going into the 486 era.