You cannot download a PS2 memory card. They are physical hardware devices (8MB MagicGate encrypted flash memory), not software files.
.mem files) on your storage..mem or converted saves from sites like GameFAQs (personal use).Old USB/Parallel port adapters to move saves between PS2 card and PC. Hard to find, driver issues on modern OS.
Recommendation: For original hardware, buy a genuine Sony 8MB card. For convenience/preservation, use PCSX2/AetherSX2.