Hypersynth has released the Hcard Series of expansion cartridges for vintage synths:
You can check out all three on their website but here's more details in their own words on the cartridge for the Yamaha DX7...
Hypersynth multibank cartridge Hcard-701 is specially designed for expanding the memory of Yamaha DX7 synthesizer. DX7 voice memory is limited to 32 presets (1 bank), which could be upgraded to 64 presets by adding an external Yamaha "Data RAM" cartridge. "Data RAM" is discontinued, rare, expensive and It relies on battery for data retention. These flaws make it not a good choice for DX lovers in modern age. "Hcard-701" can be used as a drop in replacement for Yamaha "DATA RAM" cartridge. it stores up to 100 banks without the worry of battery life and data loss.
-Memory size: Up to 100 banks (3200 presets).
-Instant access to different banks using touch buttons.
-Two digits bank indicator display.
-No need for battery.
-Drop in replacement for Yamaha "data RAM" and "Voice ROM" cartridge.
-Up to 24 pre-programmed soundbanks.
-Hidden "Memory Protect" option.
-External display support for listing all 32 presets in selected bank.
"Hcard-701" comes with default DX7 factory soundbanks, plus 16 soundbanks which selected carefully out of thousands available free banks for DX7. These sounds banks are categorized in a way to simplify the workflow of sound selection.
Pricing and Availability:
A portable and low cost entry into the world of N.I. Komplete
Two (well, three) new products from Verbos