Hi,
I have experience for 15+ years in electronics/embedded development. I have several years of advanced AVR/arduino development, including library development from scratch. Practically all Arduino AVR boards used, like: 2009, 2010, UNO, MEGA, NANO, MICRO, MINI, etc. Several shields used like Ethernet (W5100, ENC28J60, etc.) with various IP protocols implementation, various graphical TFTs with and without touchscreen and various BUS types (parallel, SPI, I2C, etc.), all kinds of sensors and buses, serial and parallel memories, etc.
I have developed previous projects with arduinos acting as PS/2 keyboards and I can easily implement your project too. This will be tested in a real live environment with a native PC with PS/2 interface running W98.
As for how/where to store the keys to send through PS/2, I think the best approach would be an SD card (virtually no limit on the amount of data stored) - a file would be generated in a PC with a specific format (like 1 key per line or similar, that we would agree later), saved to the SD card and put into this project's device, device powered up and card initialized, when a button was pushed in the device, the file contents would be sent sequentially and until EOF to the PS/2 host (with a programmed delay between chars).
Before any payment is made, I'll provide a video demoing all the final implemented project.
If you are interested in my bid, feel free to contact me.
Regards,
Carlos.