try sim lim tower, you can get the individual parts there. 3.5mm jack and 2 1/4' mono phone plug.
Then hope over to sim lim square 3rd floor, hung bros, get a stereo cable(2 core and 1 ground, the ground will be the part that wrapped around the 2 core once you stripped the cable of its insulation)
Additional, get some heat shrink from SLT as well, to cover up any exposed part(if theres any, after soldering)
for the stereo cable, at one end, stripped the insulation, separate the 2 core and the ground. The 2 wires will be soldered to the tip and ring of the 3.5 mm jack and the ground will be to the sleeve.
At the other end of the stereo cable, the 2 wires will be soldered to individual 1/4' mono phone plug's tip. For ground connection, split the ground from the stereo cable and solder it to individual mono plug's sleeve
theres another way to get the cable though, easier then the above.
In homefix or any supermarket electrical section, you can find a cable where one end is the female stereo jack and the other end, a male 1/8' stereo phone plug.
Get those kinda, chopped off the end with the male 1/8' plug and resolder it to 2 separate mono 1/4' phone plug
one thing to note is that diy style Y cable wont look as good as the one in the picture, but it will work as well
iam away from my working table now, if you cant visualise the above, give me some time, i will do a mock up with the cable, female jack and male plug(without soldering) and take some pics
