Also be careful that the females are wried correctly. You want an "insert" style splitter where the TS male is wired to the TS of one of the females and the other female get the RS of the male wired to its TS. There are splitters that wire both the T and R of the male to the T of both females (which you do not want).
Off the self, at the OT 6.35mm TRS to 3.5mm TRS, then a 3.5mm insert cable, the 3.5mm TS.
Something like:
http://www.sweetwater.com/store/detail/MHE310/plus
http://www.sweetwater.com/store/detail/YMM261/Other than that, solder up your own.
I find a lot of single cable solutions on the market that have the 6.35mm and 3.5mm in the opposite positions of what is needed for this application.