I don't think it exists I am afraid.
But having 4gb in an old DDR1 system seems quite a lot, I think you'd be really limited by the CPU (I can't think of a CPU that runs on DDR1 that would take advantage of 4gb, only in rare circumstances)
I'd imagine it would also cost around £100 to £120 for it as 2 x 1gb of DDR1 is £45 to £50. For £100 you could pick up an older core 2 duo setup, as in motherboard ram and CPU?