Someone doesn't seem to have a spare 4521, however the 4521 is not a critical part and can be substituted with a small circuit comprising of a 1/2 x 74LS123, 220k resistor, 10uF cap as per the 1011 microbee disk controller or even a humble 555 with a few bits.
You could in fact use a manually controlled toggle switch (every time you hear the disk drive head load). LOL!
FUTURELEC has some DIP 4521
They also have a variety of SMD to DIP adapters at seemingly a good price.
SMD Adapters (futurlec.com)
You could in fact use a manually controlled toggle switch (every time you hear the disk drive head load). LOL!
FUTURELEC has some DIP 4521
They also have a variety of SMD to DIP adapters at seemingly a good price.
SMD Adapters (futurlec.com)