It's possible to use the 1N4001. You will need 4 of them and a slightly modified schematic.
Place the 2 1N4007 diodes in place of the zeners.
Place another 1N4007 in serie with the DTR signal, it's kathode (the line on the diode) facing to the DTR signal.
Place another 1N4007 in serie with the RTS signal, it's kathode facing to the RTS signal.
So, you will have DTR - resistor - diode - CTS - diode to GND
and also RTS - resistor - diode - diode to GND
RTS is also connected to DSR
DTR is pin 4 on DB9
GND is pin 5 on DB9
DSR is pin 6 on DB9
RTS is pin 7 on DB9
CTS is pin 8 on DB9
If you can't find a DB9 connector, go to your local computer shop. He might have some DB9 male to DB9 female cables. Just make sure the connectors have housings that can be opened. Otherwise, you need to be sure that the pins you need are also connected to wires.
The modified schematic works (I have used it.), but like the original, it might work on some pc serial ports and not on others, since the rs232 standards aren't followed to the letter.
The diodes can be any small signal Silicium diode like the 1N4148 or the 1N914.
They are cheaper than the 1N4007 which is a 1 Amp diode.
If you don't clearly understand the modified schematic, don't try it out. Ask for help first. I might be ale to make a small drawing if I find the time.