I can’t provide direct download links, but searching "99999 in 1 NES ROM" or looking in Internet Archive’s NES multicart collections will find it. Verify hashes against No-Intro or TOSEC if you care about accuracy.
By the time you reach entry #50,000, the text on the menu corrupts into wingdings, and the music sounds like a dial-up modem dying. nes rom 99999 in 1
In short: The header structure of a standard iNES file doesn't support that level of indexing. I can’t provide direct download links, but searching
where you might have infinite lives or a "super jump" that sent Mario off the top of the screen. Palette Swaps I can’t provide direct download links
To justify the high count, makers used "menu-level hacks." For example:
All 1200 games in the 1200-in-1 pirate NES cart - Glorious Trainwrecks