Re: How to access "EXTRA" available RAM in the C-128......

I don't think you are going to find any significant RAM in any of
those ports. The VDC RAM can be accessed from BASIC by using a
certain SYS statement, but I can't remember the memory address and I'm
too lazy to google for it. But that is assuming you are in 128 Mode.
In 64 Mode, it is still possible, but a bit more complicated.
.