Some cable makers will actually make for you a Y adapter. Voodoo, Cardas, etc.
I was going to do exactly this notion... but kept trying out this and that el cheapo Y's instead.
Rather than spend around $200 for a connection to my sub, I finally settled on Ye Olde Rat Shackeys $6 Gold Series Y.
For $75 you can get one premade from that co which makes everything you need to DIY your own ICs, etc. Gosh I can't think of the name right now. I will though.
Unless... and perhaps not even then, you get a Y made by the same folks of whose cabling you perfer now, they're all gonna sound different, aren't they?
Even then, if that co has changed material sources... connector sources... uses new tech, Oh, and yours have some age on them now too....
I'm saying getting identical wire to what tyou have now seems nigh on to impossible.... and primarily why I settled on the El Cheapo's.. Changing out the subs power cord was a more favorable process and result.
The couple inches of Y wasn't nearly the change that the 12 ft of IC to it yielded, or the upscale pc I put onto my sub.
Maybe you can have your ICs terminated into a Y by their makers!
But best of luck