Re: Marshall footswitch compatibility.
Marshalls are pretty good about being compatible with many different 2-button or 1-button footswitches (dependent on what amp needs, of course). When I had my Marshall head, I didn't get a footswitch when I bought it (used) so I made one with a Hoover vacuum cleaner switch, a 1/4" mono jack and a small enclosure. Even added a LED to it as the footswitch line fed a small amount of voltage enough to power the LED. Worked great. So, if you can't find the Marshall branded one, a generic 2-button like it will work fine.